From: Borislav Petkov <bp@alien8.de>
To: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
KVM <kvm@vger.kernel.org>, Ashish Kalra <ashish.kalra@amd.com>,
Joerg Roedel <joro@8bytes.org>,
Michael Roth <michael.roth@amd.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH 5/5] x86/CPU/AMD: Track SNP host status with cc_platform_*()
Date: Thu, 28 Mar 2024 16:39:14 +0100 [thread overview]
Message-ID: <20240328153914.GBZgWPIvLT6EXAPJci@fat_crate.local> (raw)
In-Reply-To: <ac4f34a0-036a-48b9-ab56-8257700842fc@linux.microsoft.com>
On Thu, Mar 28, 2024 at 03:24:29PM +0100, Jeremi Piotrowski wrote:
> It's not but if you set it before the check it will be set for all AMD
> systems, even if they are neither CC hosts nor CC guests.
That a problem?
It is under a CONFIG_ARCH_HAS_CC_PLATFORM...
> To leave open the possibility of an SNP hypervisor running nested.
But !CC_ATTR_GUEST_SEV_SNP doesn't mean that. It means it is not
a SEV-SNP guest.
> I thought you wanted to filter out SEV-SNP guests, which also have
> X86_FEATURE_SEV_SNP CPUID bit set.
I want to run snp_probe_rmptable_info() only on baremetal where it makes
sense.
> My understanding is that these are the cases:
>
> CPUID(SEV_SNP) | MSR(SEV_SNP) | what am I
> ---------------------------------------------
> set | set | SNP-guest
> set | unset | SNP-host
> unset | ?? | not SNP
So as you can see, we can't use X86_FEATURE_SEV_SNP for anything due to
the late disable need. So we should be moving away from it.
So we need a test for "am I a nested SNP hypervisor?"
So, can your thing clear X86_FEATURE_HYPERVISOR and thus "emulate"
baremetal?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2024-03-28 15:39 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-27 15:43 [PATCH 0/5] x86/sev: Fix SNP host late disable Borislav Petkov
2024-03-27 15:43 ` [PATCH 1/5] x86/alternatives: Remove a superfluous newline in _static_cpu_has() Borislav Petkov
2024-03-27 15:43 ` [PATCH 2/5] x86/alternatives: Catch late X86_FEATURE modifiers Borislav Petkov
2024-03-27 15:57 ` Nikolay Borisov
2024-04-03 17:59 ` Borislav Petkov
2024-03-27 15:43 ` [PATCH 3/5] x86/kvm/Kconfig: Have KVM_AMD_SEV select ARCH_HAS_CC_PLATFORM Borislav Petkov
2024-03-29 14:42 ` Tom Lendacky
2024-03-27 15:43 ` [PATCH 4/5] x86/cc: Add cc_platform_set/_clear() helpers Borislav Petkov
2024-03-29 14:46 ` Tom Lendacky
2024-03-27 15:43 ` [PATCH 5/5] x86/CPU/AMD: Track SNP host status with cc_platform_*() Borislav Petkov
2024-03-28 11:51 ` Jeremi Piotrowski
2024-03-28 13:41 ` Borislav Petkov
2024-03-28 14:24 ` Jeremi Piotrowski
2024-03-28 15:39 ` Borislav Petkov [this message]
2024-04-04 17:07 ` Jeremi Piotrowski
2024-04-24 18:46 ` Borislav Petkov
2024-03-29 14:52 ` Tom Lendacky
2024-04-03 4:15 ` [PATCH 0/5] x86/sev: Fix SNP host late disable Aithal, Srikanth
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