linux-kernel - Re: [PATCH 01/19] x86/fpu: Extend prctl() with guest permissions

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Message-ID: <87lf0ot50q.ffs@tglx>
Date:   Tue, 14 Dec 2021 01:16:21 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     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,
        pbonzini@...hat.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        yang.zhong@...el.com
Subject: Re: [PATCH 01/19] x86/fpu: Extend prctl() with guest permissions

On Tue, Dec 07 2021 at 19:03, Yang Zhong wrote:
> Similar to native permissions this doesn't actually enable the
> permitted feature. KVM is expected to install a larger kernel buffer
> and enable the feature when detecting the intention from the guest.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Jing Liu <jing2.liu@...el.com>
> Signed-off-by: Yang Zhong <yang.zhong@...el.com>
> ---
> (To Thomas) We change the definition of xstate_get_guest_group_perm()
> from xstate.h to api.h since this will be called by KVM.

No.

There is absolutely no need for that. After creating a vCPU the
permissions are frozen and readily available via
vcpu->arch.guest_fpu.perm.

Thanks,

        tglx