Re: [ANNOUNCE] kvm-20 release

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

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Christian Hesse wrote:
>> It may be the cpuid strangeness that Rusty saw.  Can you try the
>> attached patch?
>>     
>
> No, that does not help.
>   

Ah, I see it.  The Core processor does not have the STAR msr.

Can you try backing out the attached patch?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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commit 5c828f83928f186320d74627089122ebc9ea98ce
Author: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
Date:   Thu Apr 19 14:28:44 2007 +0300

    KVM: VMX: Only save/restore MSR_K6_STAR if necessary
    
    Intel hosts only support syscall/sysret in long more (and only if efer.sce
    is enabled), so only reload the related MSR_K6_STAR if the guest will
    actually be able to use it.
    
    This reduces vmexit cost by about 500 cycles (6400 -> 5870) on my setup.
    
    Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index b61d4dd..3f43f50 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -323,6 +323,16 @@ static void setup_msrs(struct kvm_vcpu *vcpu)
 		nr_skip = NR_64BIT_MSRS;
 	nr_good_msrs = vcpu->nmsrs - nr_skip;
 
+	/*
+	 * MSR_K6_STAR is only needed on long mode guests, and only
+	 * if efer.sce is enabled.
+	 */
+	--nr_good_msrs;
+#if CONFIG_X86_64
+	if (is_long_mode(vcpu) && (vcpu->shadow_efer & EFER_SCE))
+		++nr_good_msrs;
+#endif
+
 	vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR,
 		    virt_to_phys(vcpu->guest_msrs + nr_skip));
 	vmcs_writel(VM_EXIT_MSR_STORE_ADDR,

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