linux-kernel - Re: [PATCH] x86/speculation/l1tf: Exempt zeroed PTEs from XOR conversion

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Message-ID: <CA+55aFzQf3VRKtvaQCbZAt3aSkd_tSTTPNYpvRbF0XdaCaNb0g@mail.gmail.com>
Date:   Fri, 17 Aug 2018 10:05:02 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     sean.j.christopherson@...el.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Peter Anvin <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] x86/speculation/l1tf: Exempt zeroed PTEs from XOR conversion

On Fri, Aug 17, 2018 at 10:01 AM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Checking for a non-zero val in __pte_needs_invert() also resolves the
> issue.  I shied away from that change because prot_none_walk() doesn't
> pass the full PTE to __pte_needs_invert(), it only passes the pgprot_t
> bits.  This works because PAGE_NONE sets the global and accessed bits,
> but it made me nervous nonetheless.

Good point, and I do think that might merit a comment in the code.
Will add, and credit you. But I'd still prefer to just fix up just
__pte_needs_invert.

Thanks,

              Linus