linux-kernel - Re: [PATCH 2/2] x86: kvm: do not advertise stable clocksource if CPU has TSC drift BUG

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Date:	Thu, 31 Jul 2014 16:38:49 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Igor Mammedov <imammedo@...hat.com>, linux-kernel@...r.kernel.org
CC:	x86@...nel.org, hpa@...or.com, mingo@...hat.com,
	tglx@...utronix.de, kvm@...r.kernel.org, mtosatti@...hat.com
Subject: Re: [PATCH 2/2] x86: kvm: do not advertise stable clocksource if
 CPU has TSC drift BUG

Il 31/07/2014 11:47, Igor Mammedov ha scritto:
> Signed-off-by: Igor Mammedov <imammedo@...hat.com>
> ---
>  arch/x86/kvm/cpuid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 38a0afe..f519823 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -478,8 +478,9 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
>  			     (1 << KVM_FEATURE_ASYNC_PF) |
>  			     (1 << KVM_FEATURE_PV_EOI) |
> -			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
>  			     (1 << KVM_FEATURE_PV_UNHALT);
> +		if (!static_cpu_has_bug(X86_BUG_AMD_TSC_DRIFT))
> +			entry->eax |= (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
>  
>  		if (sched_info_on())
>  			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
> 

Marcelo, is there anything we can do if the VM migrates from a sane host
to a buggy one?

Paolo
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