linux-kernel - Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

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Message-ID: <87a6jeaykv.ffs@tglx>
Date:   Tue, 12 Oct 2021 20:26:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

On Tue, Oct 12 2021 at 20:25, Thomas Gleixner wrote:

> On Tue, Oct 12 2021 at 18:53, Borislav Petkov wrote:
>> On Tue, Oct 12, 2021 at 02:00:17AM +0200, Thomas Gleixner wrote:
>>>  	/*
>>> -	 * Guests with protected state can't have it set by the hypervisor,
>>> -	 * so skip trying to set it.
>>> +	 * Guest with protected state have guest_fpu == NULL which makes
>>
>> "Guests ... "
>>
>>> +	 * the swap only safe the host state. Exclude PKRU from restore as
>>
>> "save"
>
> No I meant safe, but let me rephrase it, Swap does both save and
> restore. But it's not safe to dereference a NULL pointer :)
>
>  .... makes the swap only handle the host state. Exclude PKRU from restore as

Gah. I should have looked at the context first. "save" is correct
here. Oh well...