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| author | Marcelo Tosatti <mtosatti@redhat.com> | 2013-06-11 23:31:12 -0300 |
|---|---|---|
| committer | Gleb Natapov <gleb@redhat.com> | 2013-06-12 14:24:11 +0300 |
| commit | 8915aa27d5efbb9185357175b0acf884325565f9 (patch) | |
| tree | 1ff764deecb8f617e74579c46341dce7682ff615 | |
| parent | 05988d728dcd962d50374e4e63171324163005b6 (diff) | |
| download | op-kernel-dev-8915aa27d5efbb9185357175b0acf884325565f9.zip op-kernel-dev-8915aa27d5efbb9185357175b0acf884325565f9.tar.gz | |
KVM: x86: handle idiv overflow at kvm_write_tsc
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@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
| -rw-r--r-- | arch/x86/kvm/x86.c | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6402951..737c804 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 */ |
