linux-kernel - Re: Major KVM issues with kernel 4.5 on the host

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Date:	Wed, 13 Apr 2016 22:36:34 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Marc Haber <mh+linux-kernel@...schlus.de>
Cc:	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	kvm ML <kvm@...r.kernel.org>
Subject: Re: Major KVM issues with kernel 4.5 on the host



On 13/04/2016 20:37, Marc Haber wrote:
> On Fri, Mar 18, 2016 at 11:01:46AM +0100, Paolo Bonzini wrote:
>> On 17/03/2016 19:11, Borislav Petkov wrote:
>>> I'm going to try reproducing the issue on a less "important" machine
>>> so that bisecting is less painful, but maybe you guys have an idea
>>> what's going wrong here.
>>
>> No idea, sorry. :(  Bisecting would be great.
> 
> Working on that now.
> 
>>   I'll also try reproducing and bisecting next week, in the meanwhile
>>   just having the host dmesg would help a lot.
> 
> Attached. I hope the message will get through to the list.

Didn't help, but a fresh look at the list of 4.5 patches helped.
What the hell was I thinking, I missed write_rdtscp_aux who
obviously uses MSR_TSC_AUX.

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 31346a3f20a5..1481dea15844 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -39,6 +39,7 @@
 #include <asm/kvm_para.h>
 
 #include <asm/virtext.h>
+#include <asm/vgtod.h>
 #include "trace.h"
 
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
@@ -1240,9 +1241,6 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 			wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio);
 		}
 	}
-	/* This assumes that the kernel never uses MSR_TSC_AUX */
-	if (static_cpu_has(X86_FEATURE_RDTSCP))
-		wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
 }
 
 static void svm_vcpu_put(struct kvm_vcpu *vcpu)
@@ -3847,6 +3845,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 	svm->vmcb->save.cr2 = vcpu->arch.cr2;
 
 	clgi();
+	if (static_cpu_has(X86_FEATURE_RDTSCP))
+		wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
 
 	local_irq_enable();
 
@@ -3923,6 +3923,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 		);
 
+	if (static_cpu_has(X86_FEATURE_RDTSCP))
+		wrmsrl(MSR_TSC_AUX, __getcpu());
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
 #else


Paolo