[Qemu-devel] [PULL 1/1] address_space_translate: do not cross page boundaries

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

From: Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>

The following commit:

commit 149f54b53b7666a3facd45e86eece60ce7d3b114
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Fri May 24 12:59:37 2013 +0200

    memory: add address_space_translate

breaks Xen support in QEMU, in particular the Xen mapcache. The effect
is that one Windows XP installation out of ten would end up with BSOD.

The reason is that after this commit l in address_space_rw can span a
page boundary, however qemu_get_ram_ptr still calls xen_map_cache asking
to map a single page (if block->offset == 0).

Fix the issue by reverting to the previous behaviour: do not return a
length from address_space_translate_internal that can span a page
boundary.

Also in address_space_translate do not ignore the length returned by
address_space_translate_internal.

This patch should be backported to QEMU 1.6.x.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Anthony Perard <anthony.perard@citrix.com>
Tested-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org
---
 exec.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index 2435d9e..9ad0a4b 100644
--- a/exec.c
+++ b/exec.c
@@ -325,7 +325,7 @@ address_space_translate_internal(AddressSpaceDispatch *d, hwaddr addr, hwaddr *x
                                  hwaddr *plen, bool resolve_subpage)
 {
     MemoryRegionSection *section;
-    Int128 diff;
+    Int128 diff, diff_page;
 
     section = address_space_lookup_region(d, addr, resolve_subpage);
     /* Compute offset within MemoryRegionSection */
@@ -334,7 +334,9 @@ address_space_translate_internal(AddressSpaceDispatch *d, hwaddr addr, hwaddr *x
     /* Compute offset within MemoryRegion */
     *xlat = addr + section->offset_within_region;
 
+    diff_page = int128_make64(((addr & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE) - addr);
     diff = int128_sub(section->mr->size, int128_make64(addr));
+    diff = int128_min(diff, diff_page);
     *plen = int128_get64(int128_min(diff, int128_make64(*plen)));
     return section;
 }
@@ -349,7 +351,7 @@ MemoryRegion *address_space_translate(AddressSpace *as, hwaddr addr,
     hwaddr len = *plen;
 
     for (;;) {
-        section = address_space_translate_internal(as->dispatch, addr, &addr, plen, true);
+        section = address_space_translate_internal(as->dispatch, addr, &addr, &len, true);
         mr = section->mr;
 
         if (!mr->iommu_ops) {
-- 
1.7.10.4