linux-kernel - Re: [PATCH v3 1/5] x86/boot/compressed/64: Introduce sev

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Date:   Wed, 28 Oct 2020 17:55:43 +0100
From:   Joerg Roedel <jroedel@...e.de>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Martin Radev <martin.b.radev@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] x86/boot/compressed/64: Introduce sev_status

On Wed, Oct 28, 2020 at 12:50:07PM -0400, Arvind Sankar wrote:
> On Wed, Oct 28, 2020 at 09:23:52AM +0100, Joerg Roedel wrote:
> > On Mon, Oct 26, 2020 at 07:27:06PM +0100, Borislav Petkov wrote:
> > > A couple of lines above you call get_sev_encryption_bit() which already
> > > reads MSR_AMD64_SEV. Why not set sev_status there too instead of reading
> > > that MSR again here?
> > > 
> > > It can read that MSR once and use sev_status(%rip) from then on to avoid
> > > reading that MSR multiple times...
> > 
> > Right, makes sense. I updated the patch.
> 
> Hang on, get_sev_encryption_bit() is also called from startup_32(),
> so it can't contain any 64-bit instructions to set sev_status.

Yeah, figured that out too and discussed it with Boris. Decided to leave
it as-is and add a comment why the MSR is re-read.

Thanks,

	Joerg