[Xen-devel] [PATCH v5 3/4] xen: implement guest_physmap_pin_range and guest_physmap_unpin_range

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

guest_physmap_pin_range pins a range of guest pages so that their p2m
mappings won't be changed.
guest_physmap_unpin_range unpins the previously pinned pages.
The pinning is done using one of the spare bits in the p2m ptes.

Use the newly introduce p2m_walker to implement the two functions on
ARM.
Provide empty stubs for x86.


Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


Changes in v5:
- return -EBUSY when the P2M_DMA_PIN check fails;
- rename _guest_physmap_pin_range to pin_one_pte;
- rename _guest_physmap_unpin_range to unpin_one_pte.

Changes in v4:
- use p2m_walker to implement guest_physmap_pin_range and
guest_physmap_unpin_range;
- return -EINVAL when the P2M_DMA_PIN check fails;
- change the printk into a gdprintk;
- add a comment on what type of page can be pinned.
---
 xen/arch/arm/p2m.c         |   48 ++++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/mm.h   |    4 +++
 xen/include/asm-arm/page.h |    7 +++++-
 xen/include/asm-x86/p2m.h  |   12 +++++++++++
 4 files changed, 70 insertions(+), 1 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index a9ceacf..bac6c7e 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -154,6 +154,46 @@ paddr_t p2m_lookup(struct domain *d, paddr_t paddr)
     return p2m.maddr;
 }
 
+static int pin_one_pte(lpae_t *ptep, void *arg, int level)
+{
+    lpae_t pte = *ptep;
+    ASSERT(level == 3);
+
+    if ( pte.p2m.avail & P2M_DMA_PIN )
+        return -EBUSY;
+    pte.p2m.avail |= P2M_DMA_PIN;
+    write_pte(ptep, pte);
+    return 0;
+}
+
+int guest_physmap_pin_range(struct domain *d,
+                            xen_pfn_t gpfn,
+                            unsigned int order)
+{
+    return p2m_walker(d, gpfn << PAGE_SHIFT, order,
+                      pin_one_pte, NULL);
+}
+
+static int unpin_one_pte(lpae_t *ptep, void *arg, int level)
+{
+    lpae_t pte = *ptep;
+    ASSERT(level == 3);
+
+    if ( !pte.p2m.avail & P2M_DMA_PIN )
+        return -EBUSY;
+    pte.p2m.avail &= ~P2M_DMA_PIN;
+    write_pte(ptep, pte);
+    return 0;
+}
+
+int guest_physmap_unpin_range(struct domain *d,
+                              xen_pfn_t gpfn,
+                              unsigned int order)
+{
+    return p2m_walker(d, gpfn << PAGE_SHIFT, order,
+                      unpin_one_pte, NULL);
+}
+
 int guest_physmap_mark_populate_on_demand(struct domain *d,
                                           unsigned long gfn,
                                           unsigned int order)
@@ -263,6 +303,14 @@ static int create_p2m_entries(struct domain *d,
             cur_second_offset = second_table_offset(addr);
         }
 
+        if ( third[third_table_offset(addr)].p2m.avail & P2M_DMA_PIN )
+        {
+            rc = -EINVAL;
+            gdprintk(XENLOG_WARNING, "cannot change p2m mapping for 
paddr=%"PRIpaddr
+                    " domid=%d, the page is pinned\n", addr, d->domain_id);
+            goto out;
+        }
+
         flush = third[third_table_offset(addr)].p2m.valid;
 
         /* Allocate a new RAM page and attach */
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 0b0a457..d6ae3ad 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -314,6 +314,10 @@ void free_init_memory(void);
 
 int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn,
                                           unsigned int order);
+int guest_physmap_pin_range(struct domain *d, xen_pfn_t gpfn,
+                            unsigned int order);
+int guest_physmap_unpin_range(struct domain *d, xen_pfn_t gpfn,
+                              unsigned int order);
 
 extern void put_page_type(struct page_info *page);
 static inline void put_page_and_type(struct page_info *page)
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 41e9eff..c08cfca 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -153,11 +153,16 @@ typedef struct {
     unsigned long hint:1;       /* In a block of 16 contiguous entries */
     unsigned long sbz2:1;
     unsigned long xn:1;         /* eXecute-Never */
-    unsigned long avail:4;      /* Ignored by hardware */
+    unsigned long avail:4;      /* Ignored by hardware, see below */
 
     unsigned long sbz1:5;
 } __attribute__((__packed__)) lpae_p2m_t;
 
+/* Xen "avail" bits allocation in third level entries */
+#define P2M_DMA_PIN     (1<<0)  /* The page has been "pinned": the hypervisor
+                                   promises not to change the p2m mapping.
+                                   Only normal r/w guest RAM can be pinned. */
+
 /*
  * Walk is the common bits of p2m and pt entries which are needed to
  * simply walk the table (e.g. for debug).
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 43583b2..b08a722 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -492,6 +492,18 @@ void guest_physmap_remove_page(struct domain *d,
 /* Set a p2m range as populate-on-demand */
 int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn,
                                           unsigned int order);
+static inline int guest_physmap_pin_range(struct domain *d,
+                                          xen_pfn_t gpfn,
+                                          unsigned int order)
+{
+    return -ENOSYS;
+}
+static inline int guest_physmap_unpin_range(struct domain *d,
+                              xen_pfn_t gpfn,
+                              unsigned int order)
+{
+    return -ENOSYS;
+}
 
 /* Change types across all p2m entries in a domain */
 void p2m_change_entry_type_global(struct domain *d, 
-- 
1.7.2.5


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