Attachment 709835 Details for Bug 859282 – kvm-x86-handle-host-tsc-calibration-failure

[patch] kvm-x86-handle-host-tsc-calibration-failure

kvm-x86-handle-host-tsc-calibration-failure.patch (text/plain), 2.24 KB, created by Marcelo Tosatti on 2013-03-13 23:33:52 UTC

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Creator: Marcelo Tosatti

Created: 2013-03-13 23:33:52 UTC

Size: 2.24 KB

patch

obsolete

>
>Note: commit ID from kvm.git repo.
>
>https://git.kernel.org/cgit/virt/kvm/kvm.git/
>
>commit 03ba32cae66e3798d697e582633af2c7dd6907e5
>Author: Marcelo Tosatti <mtosatti@redhat.com>
>Date:   Mon Mar 11 23:10:24 2013 -0300
>
>    VMX: x86: handle host TSC calibration failure
>    
>    If the host TSC calibration fails, tsc_khz is zero (see tsc_init.c).
>    Handle such case properly in KVM (instead of dividing by zero).
>    
>    https://bugzilla.redhat.com/show_bug.cgi?id=859282
>    
>    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>    Signed-off-by: Gleb Natapov <gleb@redhat.com>
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 35b4912..b67985a 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -1079,6 +1079,10 @@ static void kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 this_tsc_khz)
> 	u32 thresh_lo, thresh_hi;
> 	int use_scaling = 0;
> 
>+	/* tsc_khz can be zero if TSC calibration fails */
>+	if (this_tsc_khz == 0)
>+		return;
>+
> 	/* Compute a scale to convert nanoseconds in TSC cycles */
> 	kvm_get_time_scale(this_tsc_khz, NSEC_PER_SEC / 1000,
> 			   &vcpu->arch.virtual_tsc_shift,
>@@ -1156,20 +1160,23 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
> 	ns = get_kernel_ns();
> 	elapsed = ns - kvm->arch.last_tsc_nsec;
> 
>-	/* n.b - signed multiplication and division required */
>-	usdiff = data - kvm->arch.last_tsc_write;
>+	if (vcpu->arch.virtual_tsc_khz) {
>+		/* 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;
>+		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));
>+		/* do_div() only does unsigned */
>+		asm("idivl %2; xor %%edx, %%edx"
>+		: "=A"(usdiff)
>+		: "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
> #endif
>-	do_div(elapsed, 1000);
>-	usdiff -= elapsed;
>-	if (usdiff < 0)
>-		usdiff = -usdiff;
>+		do_div(elapsed, 1000);
>+		usdiff -= elapsed;
>+		if (usdiff < 0)
>+			usdiff = -usdiff;
>+	} else
>+		usdiff = USEC_PER_SEC; /* disable TSC match window below */
> 
> 	/*
> 	 * Special case: TSC write with a small delta (1 second) of virtual

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Attachments on bug 859282: 709835