[Xen-devel] [PATCH] privcmd: MMAPBATCH: Fix error handling/reporting

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On error IOCTL_PRIVCMD_MMAPBATCH is expected to set the top nibble of
the effected MFN and return 0. Currently it leaves the MFN unmodified
and returns the number of failures. Therefore:

- reimplement remap_domain_mfn_range() using direct
  HYPERVISOR_mmu_update() calls and small batches. The xen_set_domain_pte()
  interface does not report errors and since some failures are
  expected/normal using the multicall infrastructure is too noisy.
- return 0 as expected
- writeback the updated MFN list to mmapbatch->arr not over mmapbatch,
  smashing the caller's stack.
- remap_domain_mfn_range can be static.

With this change I am able to start an HVM domain.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
---
 drivers/xen/xenfs/privcmd.c |   56 +++++++++++++++++++++++++++++++-----------
 1 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
index 263f622..110b062 100644
--- a/drivers/xen/xenfs/privcmd.c
+++ b/drivers/xen/xenfs/privcmd.c
@@ -31,14 +31,16 @@
 #include <xen/features.h>
 #include <xen/page.h>
 
+#define REMAP_BATCH_SIZE 16
+
 #ifndef HAVE_ARCH_PRIVCMD_MMAP
 static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma);
 #endif
 
 struct remap_data {
        unsigned long mfn;
-       unsigned domid;
        pgprot_t prot;
+       struct mmu_update *mmu_update;
 };
 
 static int remap_area_mfn_pte_fn(pte_t *ptep, pgtable_t token,
@@ -47,17 +49,23 @@ static int remap_area_mfn_pte_fn(pte_t *ptep, pgtable_t 
token,
        struct remap_data *rmd = data;
        pte_t pte = pte_mkspecial(pfn_pte(rmd->mfn++, rmd->prot));
 
-       xen_set_domain_pte(ptep, pte, rmd->domid);
+       rmd->mmu_update->ptr = arbitrary_virt_to_machine(ptep).maddr;
+       rmd->mmu_update->val = pte_val_ma(pte);
+       rmd->mmu_update++;
 
        return 0;
 }
 
-int remap_domain_mfn_range(struct vm_area_struct *vma, unsigned long addr,
-                          unsigned long mfn, unsigned long size,
-                          pgprot_t prot, unsigned domid)
+static int remap_domain_mfn_range(struct vm_area_struct *vma,
+                                 unsigned long addr,
+                                 unsigned long mfn, int nr,
+                                 pgprot_t prot, unsigned domid)
 {
        struct remap_data rmd;
-       int err;
+       struct mmu_update mmu_update[REMAP_BATCH_SIZE];
+       int batch;
+       unsigned long range;
+       int err = 0;
 
        prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
 
@@ -65,10 +73,29 @@ int remap_domain_mfn_range(struct vm_area_struct *vma, 
unsigned long addr,
 
        rmd.mfn = mfn;
        rmd.prot = prot;
-       rmd.domid = domid;
 
-       err = apply_to_page_range(vma->vm_mm, addr, size,
-                                 remap_area_mfn_pte_fn, &rmd);
+       while (nr) {
+               batch = min(REMAP_BATCH_SIZE, nr);
+               range = (unsigned long)batch << PAGE_SHIFT;
+
+               rmd.mmu_update = mmu_update;
+               err = apply_to_page_range(vma->vm_mm, addr, range,
+                                         remap_area_mfn_pte_fn, &rmd);
+               if (err)
+                       goto out;
+
+               err = -EFAULT;
+               if (HYPERVISOR_mmu_update(mmu_update, batch, NULL, domid) < 0)
+                       goto out;
+
+               nr -= batch;
+               addr += range;
+       }
+
+       err = 0;
+out:
+
+       flush_tlb_all();
 
        return err;
 }
@@ -157,7 +184,7 @@ static int traverse_pages(unsigned nelem, size_t size,
 {
        void *pagedata;
        unsigned pageidx;
-       int ret;
+       int ret = 0;
 
        BUG_ON(size > PAGE_SIZE);
 
@@ -207,8 +234,7 @@ static int mmap_mfn_range(void *data, void *state)
 
        rc = remap_domain_mfn_range(vma,
                                    msg->va & PAGE_MASK,
-                                   msg->mfn,
-                                   msg->npages << PAGE_SHIFT,
+                                   msg->mfn, msg->npages,
                                    vma->vm_page_prot,
                                    st->domain);
        if (rc < 0)
@@ -289,7 +315,7 @@ static int mmap_batch_fn(void *data, void *state)
        struct mmap_batch_state *st = state;
 
        if (remap_domain_mfn_range(st->vma, st->va & PAGE_MASK,
-                                  *mfnp, PAGE_SIZE,
+                                  *mfnp, 1,
                                   st->vma->vm_page_prot, st->domain) < 0) {
                *mfnp |= 0xf0000000U;
                st->err++;
@@ -361,9 +387,9 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
        up_write(&mm->mmap_sem);
 
        if (state.err > 0) {
-               ret = state.err;
+               ret = 0;
 
-               state.user = udata;
+               state.user = m.arr;
                traverse_pages(m.num, sizeof(xen_pfn_t),
                               &pagelist,
                               mmap_return_errors, &state);
-- 
1.5.6.5


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