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Fix KVM divide by zero error (rhbz 969644)

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This commit is contained in:
Josh Boyer 2013-06-12 07:37:50 -04:00
parent 972606b895
commit 1e99e37726
2 changed files with 52 additions and 0 deletions
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45
KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch Normal file
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@ -0,0 +1,45 @@
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 094b5d9..64a4b03 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1194,20 +1194,37 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
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 */

7
kernel.spec
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@ -770,6 +770,9 @@ Patch25042: x86-range-make-add_range-use-blank-slot.patch
#rhbz 950735
Patch25045: rt2800-fix-RT5390-RT3290-TX-power-settings-regression.patch
#rhbz 969644
Patch25046: KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
# END OF PATCH DEFINITIONS
%endif
@ -1484,6 +1487,9 @@ ApplyPatch x86-range-make-add_range-use-blank-slot.patch
#rhbz 950735
ApplyPatch rt2800-fix-RT5390-RT3290-TX-power-settings-regression.patch
#rhbz 969644
ApplyPatch KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
# END OF PATCH APPLICATIONS
%endif
@ -2290,6 +2296,7 @@ fi
# || ||
%changelog
* Wed Jun 12 2013 Josh Boyer <jwboyer@redhat.com>
- Fix KVM divide by zero error (rhbz 969644)
- Add fix for rt5390/rt3290 regression (rhbz 950735)
* Tue Jun 11 2013 Dave Jones <davej@redhat.com>