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Re: [RFC PATCH 1/2] xen/unpopulated-alloc: Introduce helpers for DMA allocations


On 04.06.22 00:52, Stefano Stabellini wrote:


Hello Stefano

Thank you for having a look and sorry for the late response.


On Tue, 17 May 2022, Oleksandr Tyshchenko wrote:

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Add ability to allocate unpopulated DMAable (contiguous) pages
suitable for grant mapping into. This is going to be used by gnttab
code (see gnttab_dma_alloc_pages()).

TODO: There is a code duplication in fill_dma_pool(). Also pool
oparations likely need to be protected by the lock.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
  drivers/xen/unpopulated-alloc.c | 167 ++++++++++++++++++++++++++++++++++++++++
  include/xen/xen.h               |  15 ++++
  2 files changed, 182 insertions(+)

diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c
index a39f2d3..bca0198 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -1,5 +1,6 @@
  // SPDX-License-Identifier: GPL-2.0
  #include <linux/errno.h>
+#include <linux/genalloc.h>
  #include <linux/gfp.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
@@ -16,6 +17,8 @@ static DEFINE_MUTEX(list_lock);
  static struct page *page_list;
  static unsigned int list_count;
+static struct gen_pool *dma_pool; 
+
  static struct resource *target_resource;
/* 
@@ -230,6 +233,161 @@ void xen_free_unpopulated_pages(unsigned int nr_pages, 
struct page **pages)
  }
  EXPORT_SYMBOL(xen_free_unpopulated_pages);
+static int fill_dma_pool(unsigned int nr_pages) 
+{

I think we shouldn't need to add this function at all as we should be
able to reuse fill_list even for contiguous pages. fill_list could
always call gen_pool_add_virt before returning.
First of all, I agree that fill_dma_pool() has a lot in common with fill_list(), so we indeed can avoid code duplication (this was mentioned in TODO). I am not quite sure regarding "to always call gen_pool_add_virt before returning" (does this mean that the same pages will be in the "page_list" and "dma_pool" simultaneously?), but I completely agree that we can reuse fill_list() for contiguous pages as well slightly updating it. 

Please see below.






+       struct dev_pagemap *pgmap;
+       struct resource *res, *tmp_res = NULL;
+       void *vaddr;
+       unsigned int alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
+       struct range mhp_range;
+       int ret;
+
+       res = kzalloc(sizeof(*res), GFP_KERNEL);
+       if (!res)
+               return -ENOMEM;
+
+       res->name = "Xen DMA pool";
+       res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
+
+       mhp_range = mhp_get_pluggable_range(true);
+
+       ret = allocate_resource(target_resource, res,
+                               alloc_pages * PAGE_SIZE, mhp_range.start, 
mhp_range.end,
+                               PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
+       if (ret < 0) {
+               pr_err("Cannot allocate new IOMEM resource\n");
+               goto err_resource;
+       }
+
+       /*
+        * Reserve the region previously allocated from Xen resource to avoid
+        * re-using it by someone else.
+        */
+       if (target_resource != &iomem_resource) {
+               tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
+               if (!res) {
+                       ret = -ENOMEM;
+                       goto err_insert;
+               }
+
+               tmp_res->name = res->name;
+               tmp_res->start = res->start;
+               tmp_res->end = res->end;
+               tmp_res->flags = res->flags;
+
+               ret = request_resource(&iomem_resource, tmp_res);
+               if (ret < 0) {
+                       pr_err("Cannot request resource %pR (%d)\n", tmp_res, 
ret);
+                       kfree(tmp_res);
+                       goto err_insert;
+               }
+       }
+
+       pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL);
+       if (!pgmap) {
+               ret = -ENOMEM;
+               goto err_pgmap;
+       }
+
+       pgmap->type = MEMORY_DEVICE_GENERIC;
+       pgmap->range = (struct range) {
+               .start = res->start,
+               .end = res->end,
+       };
+       pgmap->nr_range = 1;
+       pgmap->owner = res;
+
+       vaddr = memremap_pages(pgmap, NUMA_NO_NODE);
+       if (IS_ERR(vaddr)) {
+               pr_err("Cannot remap memory range\n");
+               ret = PTR_ERR(vaddr);
+               goto err_memremap;
+       }
+
+       ret = gen_pool_add_virt(dma_pool, (unsigned long)vaddr, res->start,
+                       alloc_pages * PAGE_SIZE, NUMA_NO_NODE);
+       if (ret)
+               goto err_pool;
+
+       return 0;
+
+err_pool:
+       memunmap_pages(pgmap);
+err_memremap:
+       kfree(pgmap);
+err_pgmap:
+       if (tmp_res) {
+               release_resource(tmp_res);
+               kfree(tmp_res);
+       }
+err_insert:
+       release_resource(res);
+err_resource:
+       kfree(res);
+       return ret;
+}
+
+/**
+ * xen_alloc_unpopulated_dma_pages - alloc unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages,
+               struct page **pages)
+{
+       void *vaddr;
+       bool filled = false;
+       unsigned int i;
+       int ret;


Also probably it might be better if xen_alloc_unpopulated_pages and
xen_alloc_unpopulated_dma_pages shared the implementation. Something
along these lines:

int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
{
     return _xen_alloc_unpopulated_pages(nr_pages, pages, false);
}

int xen_alloc_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages,
                struct page **pages)
{
     return _xen_alloc_unpopulated_pages(nr_pages, pages, true);
}
I think, this makes sense, although it depends on how the resulting _xen_alloc_unpopulated_pages() will look like. I'd s/_xen_alloc_unpopulated_pages/alloc_unpopulated_pages 

Please see below.




static int _xen_alloc_unpopulated_pages(unsigned int nr_pages,
         struct page **pages, bool contiguous)
{
        unsigned int i;
        int ret = 0;

     if (contiguous && !xen_feature(XENFEAT_auto_translated_physmap))
         return -EINVAL;

        /*
         * Fallback to default behavior if we do not have any suitable resource
         * to allocate required region from and as the result we won't be able 
to
         * construct pages.
         */
        if (!target_resource) {
         if (contiguous)
             return -EINVAL;
                return xen_alloc_ballooned_pages(nr_pages, pages);
     }

        mutex_lock(&list_lock);
        if (list_count < nr_pages) {
                ret = fill_list(nr_pages - list_count);
As I understand, this might not work if we need contiguous pages. The check might not be precise as "list_count" is a number of available pages in the list, which are not guaranteed to be contiguous, also the amount of pages to be added to the pool here "nr_pages - list_count" might not be enough to allocate contiguous region with "nr_pages" size. 



                if (ret)
                        goto out;
        }

     if (contiguous) {
         vaddr = (void *)gen_pool_alloc(dma_pool, nr_pages * PAGE_SIZE);

         for (i = 0; i < nr_pages; i++)
             pages[i] = virt_to_page(vaddr + PAGE_SIZE * i);
     } else {
         for (i = 0; i < nr_pages; i++) {
             struct page *pg = page_list;

             BUG_ON(!pg);
             page_list = pg->zone_device_data;
             list_count--;
             pages[i] = pg;
I think, if we keep the same pages in the "page_list" and "dma_pool" simultaneously we will need to reflect that here, otherwise we might end up reusing already allocated pages. What I mean is if we allocate pages from "dma_pool" we will need to remove them from the "page_list" as well and vice versa, so this might add a complexity to the code. I or missed something?
According to the suggestions I see two options, both follow suggestion where xen_alloc(free)_unpopulated_pages() and xen_alloc(free)_unpopulated_dma_pages() share the implementation.
1. Keep "page_list" and "dma_pool" separately. So they don't share pages. Like how it was implemented in current patch but with eliminating both TODOs. This doesn't change behavior for all users of xen_alloc_unpopulated_pages(). 

Below the diff for unpopulated-alloc.c. The patch is also available at:

https://github.com/otyshchenko1/linux/commit/1c629abc37478c108a5f4c37ae8076b766c4d5cc
diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c 
index a39f2d3..c3a86c09 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/dma-mapping.h>
 #include <linux/errno.h>
+#include <linux/genalloc.h>
 #include <linux/gfp.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
@@ -16,6 +18,8 @@ static DEFINE_MUTEX(list_lock);
 static struct page *page_list;
 static unsigned int list_count;

+static struct gen_pool *dma_pool;
+
 static struct resource *target_resource;

 /*
@@ -31,7 +35,7 @@ int __weak __init arch_xen_unpopulated_init(struct resource **res) 
        return 0;
 }

-static int fill_list(unsigned int nr_pages)
+static int fill_list(unsigned int nr_pages, bool use_pool)
 {
        struct dev_pagemap *pgmap;
        struct resource *res, *tmp_res = NULL;
@@ -125,12 +129,21 @@ static int fill_list(unsigned int nr_pages)
                goto err_memremap;
        }

-       for (i = 0; i < alloc_pages; i++) {
-               struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i);
+       if (use_pool) {
+               ret = gen_pool_add_virt(dma_pool, (unsigned long)vaddr, res->start, 
+                               alloc_pages * PAGE_SIZE, NUMA_NO_NODE);
+               if (ret) {
+                       memunmap_pages(pgmap);
+                       goto err_memremap;
+               }
+       } else {
+               for (i = 0; i < alloc_pages; i++) {
+                       struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i); 

-               pg->zone_device_data = page_list;
-               page_list = pg;
-               list_count++;
+                       pg->zone_device_data = page_list;
+                       page_list = pg;
+                       list_count++;
+               }
        }

        return 0;
@@ -149,13 +162,8 @@ static int fill_list(unsigned int nr_pages)
        return ret;
 }

-/**
- * xen_alloc_unpopulated_pages - alloc unpopulated pages
- * @nr_pages: Number of pages
- * @pages: pages returned
- * @return 0 on success, error otherwise
- */
-int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+static int alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages, 
+               bool contiguous)
 {
        unsigned int i;
        int ret = 0;
@@ -165,71 +173,167 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)          * to allocate required region from and as the result we won't be able to 
         * construct pages.
         */
-       if (!target_resource)
+       if (!target_resource) {
+               if (contiguous)
+                       return -ENODEV;
+
                return xen_alloc_ballooned_pages(nr_pages, pages);
+       }

        mutex_lock(&list_lock);
-       if (list_count < nr_pages) {
-               ret = fill_list(nr_pages - list_count);
-               if (ret)
-                       goto out;
-       }

-       for (i = 0; i < nr_pages; i++) {
-               struct page *pg = page_list;
+       if (contiguous) {
+               void *vaddr;
+               bool filled = false;
+
+               while (!(vaddr = (void *)gen_pool_alloc(dma_pool, nr_pages * PAGE_SIZE))) { 
+                       if (filled)
+                               ret = -ENOMEM;
+                       else {
+                               ret = fill_list(nr_pages, true);
+                               filled = true;
+                       }
+                       if (ret)
+                               goto out;
+               }

-               BUG_ON(!pg);
-               page_list = pg->zone_device_data;
-               list_count--;
-               pages[i] = pg;
+               for (i = 0; i < nr_pages; i++) {
+                       pages[i] = virt_to_page(vaddr + PAGE_SIZE * i);

 #ifdef CONFIG_XEN_HAVE_PVMMU
-               if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-                       ret = xen_alloc_p2m_entry(page_to_pfn(pg));
-                       if (ret < 0) {
-                               unsigned int j;
-
-                               for (j = 0; j <= i; j++) {
- pages[j]->zone_device_data = page_list;
-                                       page_list = pages[j];
-                                       list_count++;
+                       if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+                               ret = xen_alloc_p2m_entry(page_to_pfn(pages[i])); 
+                               if (ret < 0) {
+                                       /* XXX Do we need to zeroed pages[i]? */ +                                       gen_pool_free(dma_pool, (unsigned long)vaddr, +                                                       nr_pages * PAGE_SIZE); 
+                                       goto out;
                                }
-                               goto out;
                        }
+#endif
+               }
+       } else {
+               if (list_count < nr_pages) {
+                       ret = fill_list(nr_pages - list_count, false);
+                       if (ret)
+                               goto out;
                }
+
+               for (i = 0; i < nr_pages; i++) {
+                       struct page *pg = page_list;
+
+                       BUG_ON(!pg);
+                       page_list = pg->zone_device_data;
+                       list_count--;
+                       pages[i] = pg;
+
+#ifdef CONFIG_XEN_HAVE_PVMMU
+                       if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+                               ret = xen_alloc_p2m_entry(page_to_pfn(pg));
+                               if (ret < 0) {
+                                       unsigned int j;
+
+                                       for (j = 0; j <= i; j++) {
+ pages[j]->zone_device_data = page_list;
+                                               page_list = pages[j];
+                                               list_count++;
+                                       }
+                                       goto out;
+                               }
+                       }
 #endif
+               }
        }

 out:
        mutex_unlock(&list_lock);
        return ret;
 }
-EXPORT_SYMBOL(xen_alloc_unpopulated_pages);

-/**
- * xen_free_unpopulated_pages - return unpopulated pages
- * @nr_pages: Number of pages
- * @pages: pages to return
- */
-void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+static void free_unpopulated_pages(unsigned int nr_pages, struct page **pages, 
+               bool contiguous)
 {
-       unsigned int i;
-
        if (!target_resource) {
+               if (contiguous)
+                       return;
+
                xen_free_ballooned_pages(nr_pages, pages);
                return;
        }

        mutex_lock(&list_lock);
-       for (i = 0; i < nr_pages; i++) {
-               pages[i]->zone_device_data = page_list;
-               page_list = pages[i];
-               list_count++;
+
+       /* XXX Do we need to check the range (gen_pool_has_addr)? */
+       if (contiguous)
+               gen_pool_free(dma_pool, (unsigned long)page_to_virt(pages[0]), 
+                               nr_pages * PAGE_SIZE);
+       else {
+               unsigned int i;
+
+               for (i = 0; i < nr_pages; i++) {
+                       pages[i]->zone_device_data = page_list;
+                       page_list = pages[i];
+                       list_count++;
+               }
        }
+
        mutex_unlock(&list_lock);
 }
+
+/**
+ * xen_alloc_unpopulated_pages - alloc unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+       return alloc_unpopulated_pages(nr_pages, pages, false);
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_pages);
+
+/**
+ * xen_free_unpopulated_pages - return unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+       free_unpopulated_pages(nr_pages, pages, false);
+}
 EXPORT_SYMBOL(xen_free_unpopulated_pages);

+/**
+ * xen_alloc_unpopulated_dma_pages - alloc unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages, 
+               struct page **pages)
+{
+       /* XXX Handle devices which support 64-bit DMA address only for now */ 
+       if (dma_get_mask(dev) != DMA_BIT_MASK(64))
+               return -EINVAL;
+
+       return alloc_unpopulated_pages(nr_pages, pages, true);
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_dma_pages);
+
+/**
+ * xen_free_unpopulated_dma_pages - return unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages, 
+               struct page **pages)
+{
+       free_unpopulated_pages(nr_pages, pages, true);
+}
+EXPORT_SYMBOL(xen_free_unpopulated_dma_pages);
+
 static int __init unpopulated_init(void)
 {
        int ret;
@@ -237,9 +341,19 @@ static int __init unpopulated_init(void)
        if (!xen_domain())
                return -ENODEV;

+       dma_pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
+       if (!dma_pool) {
+               pr_err("xen:unpopulated: Cannot create DMA pool\n");
+               return -ENOMEM;
+       }
+
+       gen_pool_set_algo(dma_pool, gen_pool_best_fit, NULL);
+
        ret = arch_xen_unpopulated_init(&target_resource);
        if (ret) {
                pr_err("xen:unpopulated: Cannot initialize target resource\n"); 
+               gen_pool_destroy(dma_pool);
+               dma_pool = NULL;
                target_resource = NULL;
        }

[snip]
2. Drop the "page_list" entirely and use "dma_pool" for all (contiguous and non-contiguous) allocations. After all, all pages are initially contiguous in fill_list() as they are built from the resource. This changes behavior for all users of xen_alloc_unpopulated_pages() 

Below the diff for unpopulated-alloc.c. The patch is also available at:

https://github.com/otyshchenko1/linux/commit/7be569f113a4acbdc4bcb9b20cb3995b3151387a
diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c 
index a39f2d3..ab5c7bd 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/dma-mapping.h>
 #include <linux/errno.h>
+#include <linux/genalloc.h>
 #include <linux/gfp.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
@@ -13,8 +15,8 @@
 #include <xen/xen.h>

 static DEFINE_MUTEX(list_lock);
-static struct page *page_list;
-static unsigned int list_count;
+
+static struct gen_pool *dma_pool;

 static struct resource *target_resource;

@@ -36,7 +38,7 @@ static int fill_list(unsigned int nr_pages)
        struct dev_pagemap *pgmap;
        struct resource *res, *tmp_res = NULL;
        void *vaddr;
-       unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
+       unsigned int alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
        struct range mhp_range;
        int ret;

@@ -106,6 +108,7 @@ static int fill_list(unsigned int nr_pages)
          * conflict with any devices.
          */
        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+               unsigned int i;
                xen_pfn_t pfn = PFN_DOWN(res->start);

                for (i = 0; i < alloc_pages; i++) {
@@ -125,16 +128,17 @@ static int fill_list(unsigned int nr_pages)
                goto err_memremap;
        }

-       for (i = 0; i < alloc_pages; i++) {
-               struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i);
-
-               pg->zone_device_data = page_list;
-               page_list = pg;
-               list_count++;
+       ret = gen_pool_add_virt(dma_pool, (unsigned long)vaddr, res->start,
+                       alloc_pages * PAGE_SIZE, NUMA_NO_NODE);
+       if (ret) {
+               pr_err("Cannot add memory range to the pool\n");
+               goto err_pool;
        }

        return 0;

+err_pool:
+       memunmap_pages(pgmap);
 err_memremap:
        kfree(pgmap);
 err_pgmap:
@@ -149,51 +153,49 @@ static int fill_list(unsigned int nr_pages)
        return ret;
 }

-/**
- * xen_alloc_unpopulated_pages - alloc unpopulated pages
- * @nr_pages: Number of pages
- * @pages: pages returned
- * @return 0 on success, error otherwise
- */
-int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+static int alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages, 
+               bool contiguous)
 {
        unsigned int i;
        int ret = 0;
+       void *vaddr;
+       bool filled = false;

        /*
         * Fallback to default behavior if we do not have any suitable resource          * to allocate required region from and as the result we won't be able to 
         * construct pages.
         */
-       if (!target_resource)
+       if (!target_resource) {
+               if (contiguous)
+                       return -ENODEV;
+
                return xen_alloc_ballooned_pages(nr_pages, pages);
+       }

        mutex_lock(&list_lock);
-       if (list_count < nr_pages) {
-               ret = fill_list(nr_pages - list_count);
+
+       while (!(vaddr = (void *)gen_pool_alloc(dma_pool, nr_pages * PAGE_SIZE))) { 
+               if (filled)
+                       ret = -ENOMEM;
+               else {
+                       ret = fill_list(nr_pages);
+                       filled = true;
+               }
                if (ret)
                        goto out;
        }

        for (i = 0; i < nr_pages; i++) {
-               struct page *pg = page_list;
-
-               BUG_ON(!pg);
-               page_list = pg->zone_device_data;
-               list_count--;
-               pages[i] = pg;
+               pages[i] = virt_to_page(vaddr + PAGE_SIZE * i);

 #ifdef CONFIG_XEN_HAVE_PVMMU
                if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-                       ret = xen_alloc_p2m_entry(page_to_pfn(pg));
+                       ret = xen_alloc_p2m_entry(page_to_pfn(pages[i]));
                        if (ret < 0) {
-                               unsigned int j;
-
-                               for (j = 0; j <= i; j++) {
- pages[j]->zone_device_data = page_list;
-                                       page_list = pages[j];
-                                       list_count++;
-                               }
+                               /* XXX Do we need to zeroed pages[i]? */
+                               gen_pool_free(dma_pool, (unsigned long)vaddr, 
+                                               nr_pages * PAGE_SIZE);
                                goto out;
                        }
                }
@@ -204,32 +206,89 @@ int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages) 
        mutex_unlock(&list_lock);
        return ret;
 }
-EXPORT_SYMBOL(xen_alloc_unpopulated_pages);

-/**
- * xen_free_unpopulated_pages - return unpopulated pages
- * @nr_pages: Number of pages
- * @pages: pages to return
- */
-void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+static void free_unpopulated_pages(unsigned int nr_pages, struct page **pages, 
+               bool contiguous)
 {
-       unsigned int i;
-
        if (!target_resource) {
+               if (contiguous)
+                       return;
+
                xen_free_ballooned_pages(nr_pages, pages);
                return;
        }

        mutex_lock(&list_lock);
-       for (i = 0; i < nr_pages; i++) {
-               pages[i]->zone_device_data = page_list;
-               page_list = pages[i];
-               list_count++;
+
+       /* XXX Do we need to check the range (gen_pool_has_addr)? */
+       if (contiguous)
+               gen_pool_free(dma_pool, (unsigned long)page_to_virt(pages[0]), 
+                               nr_pages * PAGE_SIZE);
+       else {
+               unsigned int i;
+
+               for (i = 0; i < nr_pages; i++)
+                       gen_pool_free(dma_pool, (unsigned long)page_to_virt(pages[i]), 
+                                       PAGE_SIZE);
        }
+
        mutex_unlock(&list_lock);
 }
+
+/**
+ * xen_alloc_unpopulated_pages - alloc unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+       return alloc_unpopulated_pages(nr_pages, pages, false);
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_pages);
+
+/**
+ * xen_free_unpopulated_pages - return unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+       free_unpopulated_pages(nr_pages, pages, false);
+}
 EXPORT_SYMBOL(xen_free_unpopulated_pages);

+/**
+ * xen_alloc_unpopulated_dma_pages - alloc unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages, 
+               struct page **pages)
+{
+       /* XXX Handle devices which support 64-bit DMA address only for now */ 
+       if (dma_get_mask(dev) != DMA_BIT_MASK(64))
+               return -EINVAL;
+
+       return alloc_unpopulated_pages(nr_pages, pages, true);
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_dma_pages);
+
+/**
+ * xen_free_unpopulated_dma_pages - return unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages, 
+               struct page **pages)
+{
+       free_unpopulated_pages(nr_pages, pages, true);
+}
+EXPORT_SYMBOL(xen_free_unpopulated_dma_pages);
+
 static int __init unpopulated_init(void)
 {
        int ret;
@@ -237,9 +296,19 @@ static int __init unpopulated_init(void)
        if (!xen_domain())
                return -ENODEV;

+       dma_pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
+       if (!dma_pool) {
+               pr_err("xen:unpopulated: Cannot create DMA pool\n");
+               return -ENOMEM;
+       }
+
+       gen_pool_set_algo(dma_pool, gen_pool_best_fit, NULL);
+
        ret = arch_xen_unpopulated_init(&target_resource);
        if (ret) {
                pr_err("xen:unpopulated: Cannot initialize target resource\n"); 
+               gen_pool_destroy(dma_pool);
+               dma_pool = NULL;
                target_resource = NULL;
        }

[snip]
I think, regarding on the approach we would likely need to do some renaming for fill_list, page_list, list_lock, etc. 


Both options work in my Arm64 based environment, not sure regarding x86.
Or do we have another option here?
I would be happy to go any route. What do you think?




     #ifdef CONFIG_XEN_HAVE_PVMMU
             if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                 ret = xen_alloc_p2m_entry(page_to_pfn(pg));
                 if (ret < 0) {
                     unsigned int j;

                     for (j = 0; j <= i; j++) {
                         pages[j]->zone_device_data = page_list;
                         page_list = pages[j];
                         list_count++;
                     }
                     goto out;
                 }
             }
     #endif
         }
     }

out:
        mutex_unlock(&list_lock);
        return ret;
}

        


+       if (!dma_pool)
+               return -ENODEV;
+
+       /* XXX Handle devices which support 64-bit DMA address only for now */
+       if (dma_get_mask(dev) != DMA_BIT_MASK(64))
+               return -EINVAL;
+
+       while (!(vaddr = (void *)gen_pool_alloc(dma_pool, nr_pages * 
PAGE_SIZE))) {
+               if (filled)
+                       return -ENOMEM;
+               else {
+                       ret = fill_dma_pool(nr_pages);
+                       if (ret)
+                               return ret;
+
+                       filled = true;
+               }
+       }
+
+       for (i = 0; i < nr_pages; i++)
+               pages[i] = virt_to_page(vaddr + PAGE_SIZE * i);
+
+       return 0;
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_dma_pages);
+
+/**
+ * xen_free_unpopulated_dma_pages - return unpopulated DMAable pages
+ * @dev: valid struct device pointer
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages,
+               struct page **pages)
+{
+       void *vaddr;
+
+       if (!dma_pool)
+               return;
+
+       vaddr = page_to_virt(pages[0]);
+
+       gen_pool_free(dma_pool, (unsigned long)vaddr, nr_pages * PAGE_SIZE);
+}
+EXPORT_SYMBOL(xen_free_unpopulated_dma_pages);
+
  static int __init unpopulated_init(void)
  {
        int ret;
@@ -241,8 +399,17 @@ static int __init unpopulated_init(void)
        if (ret) {
                pr_err("xen:unpopulated: Cannot initialize target resource\n");
                target_resource = NULL;
+               return ret;
        }
+ dma_pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE); 
+       if (!dma_pool) {
+               pr_err("xen:unpopulated: Cannot create DMA pool\n");
+               return -ENOMEM;
+       }
+
+       gen_pool_set_algo(dma_pool, gen_pool_best_fit, NULL);
+
        return ret;
  }
  early_initcall(unpopulated_init);
diff --git a/include/xen/xen.h b/include/xen/xen.h
index a99bab8..a6a7a59 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -52,9 +52,15 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
  extern u64 xen_saved_max_mem_size;
  #endif
+struct device; 
+
  #ifdef CONFIG_XEN_UNPOPULATED_ALLOC
  int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages);
  void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages);
+int xen_alloc_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages,
+               struct page **pages);
+void xen_free_unpopulated_dma_pages(struct device *dev, unsigned int nr_pages,
+               struct page **pages);
  #include <linux/ioport.h>
  int arch_xen_unpopulated_init(struct resource **res);
  #else
@@ -69,6 +75,15 @@ static inline void xen_free_unpopulated_pages(unsigned int 
nr_pages,
  {
        xen_free_ballooned_pages(nr_pages, pages);
  }
+static inline int xen_alloc_unpopulated_dma_pages(struct device *dev,
+               unsigned int nr_pages, struct page **pages)
+{
+       return -1;
+}
+static inline void xen_free_unpopulated_dma_pages(struct device *dev,
+               unsigned int nr_pages, struct page **pages)
+{
+}
  #endif

Given that we have these stubs, maybe we don't need to #ifdef the so
much code in the next patch


ok, I will analyze


--
Regards,

Oleksandr Tyshchenko

 

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