From: Arvind Sankar <nivedita@alum.mit.edu>
To: Joerg Roedel <jroedel@suse.de>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Joerg Roedel <joro@8bytes.org>,
x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Kees Cook <keescook@chromium.org>,
Martin Radev <martin.b.radev@gmail.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path
Date: Tue, 20 Oct 2020 12:04:28 -0400 [thread overview]
Message-ID: <20201020160428.GA3233355@rani.riverdale.lan> (raw)
In-Reply-To: <20201020154812.GB22179@suse.de>
On Tue, Oct 20, 2020 at 05:48:12PM +0200, Joerg Roedel wrote:
> On Tue, Oct 20, 2020 at 10:12:59AM -0400, Arvind Sankar wrote:
> > On Tue, Oct 20, 2020 at 02:18:54PM +0200, Joerg Roedel wrote:
> > Why use r10-r12 rather than the caller-save registers? Even for the head
> > code where you need to perserve the cr3 value you can just return it in
> > rax?
>
> It can surely be optimized, but it makes the code less robust. This
> function is only called from assembly so the standard x86-64 calling
> conventions might not be followed strictly. I think its better to make
> as few assumptions as possible about the calling code to avoid
> regressions. Changes to the head code are not necessarily tested with
> SEV/SEV-ES guests by developers.
>
> Regards,
>
> Joerg
This is called from both assembly and C, but anyway, you're already
assuming r10 and r11 can be clobbered safely, and you just took out the
save/restores in set_sev_encryption_mask, which is actually called only
from assembly.
next prev parent reply other threads:[~2020-10-20 16:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 12:18 [PATCH v2 0/5] x86/sev-es: Mitigate some HV attack vectors Joerg Roedel
2020-10-20 12:18 ` [PATCH v2 1/5] x86/boot/compressed/64: Introduce sev_status Joerg Roedel
2020-10-20 12:18 ` [PATCH v2 2/5] x86/boot/compressed/64: Add CPUID sanity check to early #VC handler Joerg Roedel
2020-10-20 12:18 ` [PATCH v2 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path Joerg Roedel
2020-10-20 14:12 ` Arvind Sankar
2020-10-20 15:48 ` Joerg Roedel
2020-10-20 16:04 ` Arvind Sankar [this message]
2020-10-21 12:49 ` Joerg Roedel
2020-10-20 12:18 ` [PATCH v2 4/5] x86/head/64: Check SEV encryption before switching to kernel page-table Joerg Roedel
2020-10-20 12:18 ` [PATCH v2 5/5] x86/sev-es: Do not support MMIO to/from encrypted memory Joerg Roedel
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