This is a note to let you know that I've just added the patch titled
KVM: x86: handle idiv overflow at kvm_write_tsc
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8915aa27d5efbb9185357175b0acf884325565f9 Mon Sep 17 00:00:00 2001
From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Date: Tue, 11 Jun 2013 23:31:12 -0300
Subject: KVM: x86: handle idiv overflow at kvm_write_tsc
From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
commit 8915aa27d5efbb9185357175b0acf884325565f9 upstream.
Its possible that idivl overflows (due to large delta stored in usdiff,
valid scenario).
Create an exception handler to catch the overflow exception (division by zero
is protected by vcpu->arch.virtual_tsc_khz check), and interpret it accordingly
(delta is larger than USEC_PER_SEC).
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=969644
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
Signed-off-by: Philipp Hahn <hahn@xxxxxxxxxxxxx>
Tested-by: Philipp Hahn <hahn@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1196,20 +1196,37 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu
elapsed = ns - kvm->arch.last_tsc_nsec;
if (vcpu->arch.virtual_tsc_khz) {
+ int faulted = 0;
+
/* n.b - signed multiplication and division required */
usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
/* do_div() only does unsigned */
- asm("idivl %2; xor %%edx, %%edx"
- : "=A"(usdiff)
- : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
+ asm("1: idivl %[divisor]\n"
+ "2: xor %%edx, %%edx\n"
+ " movl $0, %[faulted]\n"
+ "3:\n"
+ ".section .fixup,\"ax\"\n"
+ "4: movl $1, %[faulted]\n"
+ " jmp 3b\n"
+ ".previous\n"
+
+ _ASM_EXTABLE(1b, 4b)
+
+ : "=A"(usdiff), [faulted] "=r" (faulted)
+ : "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz));
+
#endif
do_div(elapsed, 1000);
usdiff -= elapsed;
if (usdiff < 0)
usdiff = -usdiff;
+
+ /* idivl overflow => difference is larger than USEC_PER_SEC */
+ if (faulted)
+ usdiff = USEC_PER_SEC;
} else
usdiff = USEC_PER_SEC; /* disable TSC match window below */
Patches currently in stable-queue which might be from mtosatti@xxxxxxxxxx are
queue-3.10/kvm-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
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