3.10-stable review patch. If anyone has any objections, please let me know.
------------------ From: Marcelo Tosatti <[email protected]> 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 <[email protected]> Signed-off-by: Gleb Natapov <[email protected]> Signed-off-by: Philipp Hahn <[email protected]> Tested-by: Philipp Hahn <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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 */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
