linux-kernel - Re: [PATCH v1 1/2] x86/mm, kexec: Fix memory corruption with SME on successive kexecs

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Message-ID: <CA+55aFwRykCYz0p1WTJeehcpXwqN10UGOJrMcTRB4zUxt=D5ng@mail.gmail.com>
Date:   Thu, 27 Jul 2017 10:34:32 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Young <dyoung@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH v1 1/2] x86/mm, kexec: Fix memory corruption with SME on
 successive kexecs

On Thu, Jul 27, 2017 at 7:15 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
>
> I can #ifdef the wbinvd based on whether AMD_MEM_ENCRYPT is configured
> or not so that the wbinvd is avoided if not configured.

I suspect an ifdef will be useless, since things like distro kernels
tend to enable everything.

So it should probably be disabled dynamically, and only done if the
AMD memory encryption thing has actually been active.

[ There have also been various actual errata with wbinvd, so there
tends to be a non-performance reason to try to avoid it unless
strictly required ]

               Linus