linux-kernel - Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

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Date:   Thu, 18 Oct 2018 10:47:47 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...capital.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

On 10/18/2018 09:48 AM, Andy Lutomirski wrote:
>>>> We might want to do this for cleanliness reasons...  Maybe.
>>>>
>>>> But this *should* have no practical effects.  Kernel threads have no
>>>> real 'mm' and no user pages.  They should not have do access to user
>>>> mappings.  Protection keys *only* apply to user mappings.  Thus,
>>>> logically, they should never be affected by PKRU values.
>>>>
>>>> So I'm kinda missing the point of the patch.
>>> use_mm().
>> So. I would drop that patch from queue. Anyone feels different about it?
>>
> I think we *do* want the patch. It’s a bugfix for use_mm users, right?

Yes, we need it.  I was being dense and Andy kindly reminded me of the
point of the patch.