KVM: MMU: calculate correct gfn for small host pages backing large guest pages
In Documentation/kvm/mmu.txt:
gfn:
Either the guest page table containing the translations shadowed by this
page, or the base page frame for linear translations. See role.direct.
But in function FNAME(fetch)(), sp->gfn is incorrect when one of following
situations occurred:
1) guest is 32bit paging and the guest PDE maps a 4-MByte page
(backed by 4k host pages), FNAME(fetch)() miss handling the quadrant.
And if guest use pse-36, "table_gfn = gpte_to_gfn(gw->ptes[level - delta]);"
is incorrect.
2) guest is long mode paging and the guest PDPTE maps a 1-GByte page
(backed by 4k or 2M host pages).
So we fix it to suit to the document and suit to the code which
requires sp->gfn correct when sp->role.direct=1.
We use the goal mapping gfn(gw->gfn) to calculate the base page frame
for linear translations, it is simple and easy to be understood.
Reported-by: Marcelo Tosatti <mtosatti@redhat.com>
Reported-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 2ee7060..1f7f5dd 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -339,10 +339,13 @@
direct = 1;
if (!is_dirty_gpte(gw->ptes[level - delta]))
access &= ~ACC_WRITE_MASK;
- table_gfn = gpte_to_gfn(gw->ptes[level - delta]);
- /* advance table_gfn when emulating 1gb pages with 4k */
- if (delta == 0)
- table_gfn += PT_INDEX(addr, level);
+ /*
+ * It is a large guest pages backed by small host pages,
+ * So we set @direct(@shadow_page->role.direct)=1, and
+ * set @table_gfn(@shadow_page->gfn)=the base page frame
+ * for linear translations.
+ */
+ table_gfn = gw->gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
access &= gw->pte_access;
} else {
direct = 0;