linux-kernel - Re: [PATCH 02/19] x86/fpu: Prepare KVM for dynamically enabled states

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Message-ID: <878rwovhnh.ffs@tglx>
Date:   Mon, 13 Dec 2021 13:00:34 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Yang Zhong <yang.zhong@...el.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com
Subject: Re: [PATCH 02/19] x86/fpu: Prepare KVM for dynamically enabled states

On Mon, Dec 13 2021 at 10:12, Paolo Bonzini wrote:
> On 12/8/21 01:03, Yang Zhong wrote:
>>    - user_xfeatures
>> 
>>      Track which features are currently enabled for the vCPU
>
> Please rename to alloc_xfeatures

That name makes no sense at all. This has nothing to do with alloc.

>>    - user_perm
>> 
>>      Copied from guest_perm of the group leader thread. The first
>>      vCPU which does the copy locks the guest_perm
>
> Please rename to perm_xfeatures.

All of that is following the naming conventions in the FPU code related
to permissions etc.

>>    - realloc_request
>> 
>>      KVM sets this field to request dynamically-enabled features
>>      which require reallocation of @fpstate
>
> This field should be in vcpu->arch, and there is no need for 
> fpu_guest_realloc_fpstate.  Rename __xfd_enable_feature to 
> fpu_enable_xfd_feature and add it to the public API, then just do
>
> 	if (unlikely(vcpu->arch.xfd_realloc_request)) {
> 		u64 request = vcpu->arch.xfd_realloc_request;
> 		ret = fpu_enable_xfd(request, enter_guest);
> 	}
>
> to kvm_put_guest_fpu.

Why? Yet another export of FPU internals just because?

Also what clears the reallocation request and what is the @enter_guest
argument supposed to help with?

I have no idea what you are trying to achieve.

Thanks,

        tglx