Re: [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest permissions

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Subject: Re: [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest permissions
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Tue, 14 Dec 2021 11:37:39 +0100
Cc: Jing Liu <jing2.liu@xxxxxxxxxxxxxxx>, "Zhong, Yang" <yang.zhong@xxxxxxxxx>, "x86@xxxxxxxxxx" <x86@xxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx" <kvm@xxxxxxxxxxxxxxx>, "Christopherson,, Sean" <seanjc@xxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
In-reply-to: <BN9PR11MB5276B6158AC37CA38201D4308C759@BN9PR11MB5276.namprd11.prod.outlook.com>
References: <20211214022825.563892248@linutronix.de> <20211214024947.818549574@linutronix.de> <BN9PR11MB5276B6158AC37CA38201D4308C759@BN9PR11MB5276.namprd11.prod.outlook.com>
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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

References:
- [patch 0/6] x86/fpu: Preparatory changes for guest AMX support
  - From: Thomas Gleixner
- [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest permissions
  - From: Thomas Gleixner
- RE: [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest permissions
  - From: Tian, Kevin

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