linux-kernel - Re: [PATCH 1/2] KVM: VMX: Use kvm_read

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Message-ID: <f8beddb6-5139-07e7-c880-6767b1e9ba40@intel.com>
Date:   Wed, 12 Apr 2023 16:02:37 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: VMX: Use kvm_read_cr4() to get cr4 value

On 4/11/2023 1:11 AM, Sean Christopherson wrote:
> On Mon, Apr 10, 2023, Xiaoyao Li wrote:
>> Directly use vcpu->arch.cr4 is not recommended since it gets stale value
>> if the cr4 is not available.
>>
>> Use kvm_read_cr4() instead to ensure correct value.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> ---
>>   arch/x86/kvm/vmx/vmx.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index d7bf14abdba1..befa2486836b 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -3431,7 +3431,7 @@ static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>>   
>>   void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>>   {
>> -	unsigned long old_cr4 = vcpu->arch.cr4;
>> +	unsigned long old_cr4 = kvm_read_cr4(vcpu);
> 
> Ha!  I've been tempted to change this multiple times, but always thought I was
> just being a bit obsessive :-)
> 
> Patches look good, but I'm going to hold them for 6.5 just in case this somehow
> causes a problem, e.g. if there's a bizzaro nested path that "works" because KVM
> _doesn't_ decache info from the current VMCS.

so you will put it in kvm-next after 6.4 merge windows?