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From: Avi Kivity <>
Subject: [PATCH 5/5] KVM: Fix bogus pagefault on writable pages
Date: Thu, 11 Jan 2007 10:07:30 -0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

If a page is marked as dirty in the guest pte, set_pte_common() can set the
writable bit on newly-instantiated shadow pte.  This optimization avoids
a write fault after the initial read fault.

However, if a write fault instantiates the pte, fix_write_pf() incorrectly
reports the fault as a guest page fault, and the guest oopses on what appears
to be a correctly-mapped page.

Fix is to detect the condition and only report a guest page fault on a user
access to a kernel page.

With the fix, a kvm guest can survive a whole night of running the kernel
hacker's screensaver (make -j9 in a loop).

Signed-off-by: Avi Kivity <>

Index: linux-2.6/drivers/kvm/paging_tmpl.h
--- linux-2.6.orig/drivers/kvm/paging_tmpl.h
+++ linux-2.6/drivers/kvm/paging_tmpl.h
@@ -274,7 +274,7 @@ static int FNAME(fix_write_pf)(struct kv
 	struct kvm_mmu_page *page;
 	if (is_writeble_pte(*shadow_ent))
-		return 0;
+		return !user || (*shadow_ent & PT_USER_MASK);
 	writable_shadow = *shadow_ent & PT_SHADOW_WRITABLE_MASK;
 	if (user) {

      parent reply	other threads:[~2007-01-11 10:07 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-11 10:02 [PATCH 0/5] KVM updates for 2.6.20 Avi Kivity
2007-01-11 10:03 ` [PATCH 1/5] KVM: Make sure there is a vcpu context loaded when destroying the mmu Avi Kivity
2007-01-11 10:04 ` [PATCH 2/5] KVM: Fix race between mmio reads and injected interrupts Avi Kivity
2007-01-11 10:05 ` [PATCH 3/5] KVM: x86 emulator: fix bit string instructions Avi Kivity
2007-01-11 10:06 ` [PATCH 4/5] KVM: Fix asm constraints with CONFIG_FRAME_POINTER=n Avi Kivity
2007-01-23  3:10   ` Herbert Xu
2007-01-11 10:07 ` Avi Kivity [this message]

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