linux-kernel - Re: [PATCH v2 15/49] KVM: x86: Zero out PV features cache when the CPUID leaf is not present

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Message-ID: <8fb52f51eb1ff52f5fe666806205cb77a98b6195.camel@redhat.com>
Date: Thu, 04 Jul 2024 21:17:36 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Hou Wenlong
 <houwenlong.hwl@...group.com>, Kechen Lu <kechenl@...dia.com>, Oliver Upton
 <oliver.upton@...ux.dev>, Binbin Wu <binbin.wu@...ux.intel.com>, Yang
 Weijiang <weijiang.yang@...el.com>, Robert Hoo <robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 15/49] KVM: x86: Zero out PV features cache when the
 CPUID leaf is not present

On Fri, 2024-05-17 at 10:38 -0700, Sean Christopherson wrote:
> Clear KVM's PV feature cache prior when processing a new guest CPUID so
> that KVM doesn't keep a stale cache entry if userspace does KVM_SET_CPUID2
> multiple times, once with a PV features entry, and a second time without.
> 
> Fixes: 66570e966dd9 ("kvm: x86: only provide PV features if enabled in guest's CPUID")
> Cc: Oliver Upton <oliver.upton@...ux.dev>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/cpuid.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index f756a91a3f2f..be1c8f43e090 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -246,6 +246,8 @@ void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *best = kvm_find_kvm_cpuid_features(vcpu);
>  
> +	vcpu->arch.pv_cpuid.features = 0;
> +
>  	/*
>  	 * save the feature bitmap to avoid cpuid lookup for every PV
>  	 * operation

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky