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

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Date:   Mon, 19 Oct 2020 18:08:01 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "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>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Martin Radev <martin.b.radev@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] x86/boot/compressed/64: Introduce sev_status

On Mon, Oct 19, 2020 at 05:59:25PM -0700, Sean Christopherson wrote:
> On Mon, Oct 19, 2020 at 05:11:17PM +0200, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@...e.de>
> > 
> > Introduce sev_status and initialize it together with sme_me_mask to have
> > an indicator which SEV features are enabled.
> > 
> > Signed-off-by: Joerg Roedel <jroedel@...e.de>
> > ---
> >  arch/x86/boot/compressed/mem_encrypt.S | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
> > index dd07e7b41b11..0effd58f0095 100644
> > --- a/arch/x86/boot/compressed/mem_encrypt.S
> > +++ b/arch/x86/boot/compressed/mem_encrypt.S
> > @@ -71,6 +71,8 @@ SYM_FUNC_END(get_sev_encryption_bit)
> >  SYM_FUNC_START(set_sev_encryption_mask)
> >  #ifdef CONFIG_AMD_MEM_ENCRYPT
> >  	push	%rbp
> > +	push	%rax
> > +	push	%rcx
> 
> There's no need to save/restore RAX and RCX, they are callee save.  This
> function is only called from C, so I doubt it's using a custom ABI.

Gah, *caller* save.  Feedback stands, my English notwithstanding.