[kernel/f17] Fix KVM divide by zero error (rhbz 969644)

[Josh Boyer]

commit 06a13386b0c9a3fe48a81645f2ffac4d659780d5
Author: Josh Boyer <jwboyer at redhat.com>
Date:   Wed Jun 12 07:37:50 2013 -0400

    Fix KVM divide by zero error (rhbz 969644)

 ...x86-handle-idiv-overflow-at-kvm_write_tsc.patch |   45 ++++++++++++++++++++
 kernel.spec                                        |    7 +++
 2 files changed, 52 insertions(+), 0 deletions(-)
---
diff --git a/KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch b/KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
new file mode 100644
index 0000000..678e829
--- /dev/null
+++ b/KVM-x86-handle-idiv-overflow-at-kvm_write_tsc.patch
@@ -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 */
+ 
diff --git a/kernel.spec b/kernel.spec
index e49c35c..041afff 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -778,6 +778,9 @@ 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
@@ -1510,6 +1513,9 @@ 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
@@ -2362,6 +2368,7 @@ fi
 #              '-'
 %changelog
 * Wed Jun 12 2013 Josh Boyer <jwboyer at redhat.com>
+- Fix KVM divide by zero error (rhbz 969644)
 - Add fix for rt5390/rt3290 regression (rhbz 950735)
 
 * Tue Jun 11 2013 Josh Boyer <jwboyer at redhat.com> - 3.9.5-101