linux-kernel - Re: [PATCH] x86/sev: Make SEV

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Message-ID: <2koe2zg26fndx6d6jcmbg6dzybbgldgrjufupj74nvmav2dmqg@w6bknhosl64h>
Date: Thu, 6 Mar 2025 10:01:17 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Borislav Petkov <bp@...en8.de>, Joerg Roedel <jroedel@...e.de>, 
	Ingo Molnar <mingo@...nel.org>, Joerg Roedel <joro@...tes.org>, x86@...nel.org, hpa@...or.com, 
	Tom Lendacky <thomas.lendacky@....com>, Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org, 
	Larry.Dewey@....com, "Alexey Gladkov (Intel)" <alexey.gladkov@...el.com>
Subject: Re: [PATCH] x86/sev: Make SEV_STATUS available via SYSFS

On Wed, Mar 05, 2025 at 08:40:29AM -0800, Dave Hansen wrote:
> On 3/5/25 07:37, Borislav Petkov wrote:
> >> So this question boils down to whether the parsing of the bits happens
> >> in kernel- or user-space. Actually there is already parsing in
> >> kernel-space to print the status bits into the kernel log:
> >>
> >> 	SEV: Status: SEV SEV-ES SEV-SNP
> >>
> >> ... which is great for a quick glance without needing any tools. The
> >> user-space tools which already exist have their own parsing of the bits
> >> and for them it is much easier to consume the raw value of the
> >> SEV_STATUS MSR. See my changes to snpguest:
> >>
> >> 	https://github.com/virtee/snpguest/pull/88/files
> > Well, I guess we can do both:
> > 
> > cat /sys/...
> > 
> > SEV_STATUS(0xdeadbeef): SEV SEV-ES SEV-SNP
> > 
> > So that people don't have to pick apart the MSR hex value.
> > 
> >> Btw, what is the equivalent on the Intel TDX side for these feature
> >> bits?
> > There is none, AFAICT. That's why the whole discussion.
> 
> TDX's history isn't as exciting as SEV.
> 
> TDX guests have CPUID to tell them that they're running that way.
> 
> TDX hosts are much more arcane. You can't _actually_ know that it's a
> TDX host until you actually start making successful SEAMCALLs and the
> TDX module answers them. But we fudge it by just looking at
> MSR_IA32_MKTME_KEYID_PARTITIONING at boot and assuming that anything
> with that MSR will be able to be a TDX host.
> 
> We've just got X86_FEATUREs for hosts and guests:
> 
> 	#define X86_FEATURE_TDX_HOST_PLATFORM ( 7*32+ 7)
> 	#define X86_FEATURE_TDX_GUEST ( 8*32+22)
> 
> and that's it.
> 
> Folks certainly _want_ something in sysfs to dump the TDX module version
> and so forth, but we've resisted the urge so far.

Alexey looking into exposing TDX module version in sysfs for both guest
and host.

I think it would be useful for guest to make attributes and TD_CTLS
available via sysfs. So far, we only dump them in dmesg on boot (see
564ea84c8c14).

-- 
  Kiryl Shutsemau / Kirill A. Shutemov