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

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Date:   Thu, 13 Apr 2023 09:23:14 +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 4/12/2023 11:03 PM, Sean Christopherson wrote:
> On Wed, Apr 12, 2023, Xiaoyao Li wrote:
>> 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?
> 
> The likely candidate is "kvm-x86 vmx", and I probably won't apply the patches until
> after v6.4-rc2 (rc2 being my preferred base for the next cycle).  But yes, the plan
> is to apply the patches after the 6.4 merge window.
> 
> Are you asking because you want to know if you need to resend for 6.5?  Or does
> the timing/location matter for some other reason, e.g. a dependency from another
> patch/series?

none of it. Just to confirm I get it. :)