linux-kernel - Re: [patch 1/6] x86/fpu: Extend fpu_xstate

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Date:   Tue, 14 Dec 2021 11:37:39 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Jing Liu <jing2.liu@...ux.intel.com>,
        "Zhong, Yang" <yang.zhong@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>
Subject: Re: [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest
 permissions

On 12/14/21 06:13, Tian, Kevin wrote:
>>    2) Permissions are frozen when the first vCPU is created to ensure
>>       consistency. Any attempt to expand permissions via the prctl() after
>>       that point is rejected.
>
> A curiosity question. Do we allow the user to reduce permissions?

No, there's no prctl for that.

Paolo