Re: [Xen-ia64-devel] [Patch] Fix for re-enabling PV-on-HVM on IPF

[DOI Tsunehisa <Doi.Tsunehisa@xxxxxxxxxxxxxx>]

Hi all,

  I've modified it, so submit the patch.

Doi.Tsunehisa@xxxxxxxxxxxxxx wrote:
> You (yamahata) said:
>>>> Probably it should looks like the following.
>>>> if (page->count_info != 1) { /* no one but us is using this page */
>>>>    put_page(page);
>>>>    goto out;
>>>> }
>>>> __set_bit(&page->count_info, _PGC_allocated);
>>>   Does `page->count_info' have to be operated with atomic ?
>> Atomic operation is safe bet.
>> XENMAPSPACE hypercall isn't performance critical.
>> If you want to be paranoia, use "if (test_and_set_bit())" to check whether
>> some else set the bit.
> 
>   I'll modify it with this policy.
> 
> Thanks,
> - Tsunehisa Doi

Signed-off-by: Tsunehisa Doi <Doi.Tsunehisa@xxxxxxxxxxxxxx>

diff -r 61eb6589e720 xen/arch/ia64/xen/mm.c
--- a/xen/arch/ia64/xen/mm.c    Tue Mar 06 21:11:37 2007 +0900
+++ b/xen/arch/ia64/xen/mm.c    Thu Mar 08 20:42:26 2007 +0900
@@ -2087,18 +2087,33 @@ arch_memory_op(int op, XEN_GUEST_HANDLE(
             break;
         case XENMAPSPACE_grant_table:
             spin_lock(&d->grant_table->lock);
+
+            if ((xatp.idx >= nr_grant_frames(d->grant_table)) &&
+                (xatp.idx < max_nr_grant_frames))
+                gnttab_grow_table(d, xatp.idx + 1);
+
             if (xatp.idx < nr_grant_frames(d->grant_table))
-                mfn = virt_to_mfn(d->grant_table->shared) + xatp.idx;
+                mfn = virt_to_mfn(d->grant_table->shared[xatp.idx]);
+
             spin_unlock(&d->grant_table->lock);
             break;
         default:
             break;
         }
 
+        if (mfn == 0) {
+            put_domain(d);
+            return -EINVAL;
+        }
+
         LOCK_BIGLOCK(d);
 
+        /* Check remapping necessity */
+        prev_mfn = gmfn_to_mfn(d, xatp.gpfn);
+        if (mfn == prev_mfn)
+            goto out;
+
         /* Remove previously mapped page if it was present. */
-        prev_mfn = gmfn_to_mfn(d, xatp.gpfn);
         if (prev_mfn && mfn_valid(prev_mfn)) {
             if (IS_XEN_HEAP_FRAME(mfn_to_page(prev_mfn)))
                 /* Xen heap frames are simply unhooked from this phys slot. */
@@ -2110,12 +2125,31 @@ arch_memory_op(int op, XEN_GUEST_HANDLE(
 
         /* Unmap from old location, if any. */
         gpfn = get_gpfn_from_mfn(mfn);
-        if (gpfn != INVALID_M2P_ENTRY)
+        if (gpfn != INVALID_M2P_ENTRY) {
+            /*
+             * guest_physmap_remove_page() (for IPF) descrements page
+             * counter and unset PGC_allocated flag,
+             * so pre-increment page counter and post-set flag inserted
+             */
+            /* pre-increment page counter */
+            if (!get_page(mfn_to_page(mfn), d))
+                goto out;
+
             guest_physmap_remove_page(d, gpfn, mfn);
+
+            /* post-set PGC_allocated flag */
+            if ((mfn_to_page(mfn)->count_info & PGC_count_mask) != 1) {
+                /* no one but us is using this page */
+                put_page(mfn_to_page(mfn));
+                goto out;
+            }
+            set_bit(_PGC_allocated, &mfn_to_page(mfn)->count_info);
+        }
 
         /* Map at new location. */
         guest_physmap_add_page(d, xatp.gpfn, mfn);
 
+    out:
         UNLOCK_BIGLOCK(d);
         
         put_domain(d);

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