From: K Prateek Nayak <kprateek.nayak@amd.com>
To: Jethro Beekman <jethro@fortanix.com>,
Ashish Kalra <Ashish.Kalra@amd.com>, <tglx@kernel.org>,
<mingo@redhat.com>, <bp@alien8.de>, <dave.hansen@linux.intel.com>,
<x86@kernel.org>, <hpa@zytor.com>, <seanjc@google.com>,
<peterz@infradead.org>, <thomas.lendacky@amd.com>,
<herbert@gondor.apana.org.au>, <davem@davemloft.net>,
<ardb@kernel.org>
Cc: <pbonzini@redhat.com>, <aik@amd.com>, <Michael.Roth@amd.com>,
<Tycho.Andersen@amd.com>, <Nathan.Fontenot@amd.com>,
<ackerleytng@google.com>, <jackyli@google.com>,
<pgonda@google.com>, <rientjes@google.com>, <jacobhxu@google.com>,
<xin@zytor.com>, <pawan.kumar.gupta@linux.intel.com>,
<babu.moger@amd.com>, <dyoung@redhat.com>, <nikunj@amd.com>,
<john.allen@amd.com>, <darwi@linutronix.de>,
<linux-kernel@vger.kernel.org>, <linux-crypto@vger.kernel.org>,
<kvm@vger.kernel.org>, <linux-coco@lists.linux.dev>
Subject: Re: [PATCH v10 3/6] x86/sev: Disable CPU hotplug while SNP is active
Date: Wed, 1 Jul 2026 22:09:28 +0530 [thread overview]
Message-ID: <8477525d-55ad-4fc4-b7c6-05bab3d7a861@amd.com> (raw)
In-Reply-To: <80f3f279-d70e-44d7-a179-c52068115e46@fortanix.com>
Hello Jethro,
On 7/1/2026 3:10 PM, Jethro Beekman wrote:
> I don't believe my concern has been addressed
>
> https://lore.kernel.org/lkml/0df3b665-3a9c-4c46-a7aa-14388e8e1577@fortanix.com/
Quoting your question:
> I think this is too broad. If I have a hypervisor that supports SNP
> virtualization, a (non-confidential) L1 guest running Linux should
> still support CPU hotplug while also running confidential L2 guests.
Ashish, Tom, correct me if I'm wrong, but I don't think KVM exposes SNP
support to L1, at least as per
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kvm/cpuid.c?h=v7.2-rc1#n1221
and only SNP initialization disables hotplug - not the other variants.
L1, running a confidential guest (SEV/SEV-ES) should still be able to
support hotplug since it doesn't go through SNP init. Only the base
hypervisor can setup the RMP tables and go through snp_prepare().
Also bsp_determine_snp() should clear CC_ATTR_HOST_SEV_SNP if it
detects X86_FEATURE_HYPERVISOR so I don't see how this can be a
problem for hotplug in L1.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/cpu/amd.c?h=v7.2-rc1#n368
--
Thanks and Regards,
Prateek
next prev parent reply other threads:[~2026-07-01 16:39 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-30 18:08 [PATCH v10 0/6] Add RMPOPT support Ashish Kalra
2026-06-30 18:09 ` [PATCH v10 1/6] x86/cpufeatures: Add X86_FEATURE_RMPOPT feature flag Ashish Kalra
2026-06-30 18:10 ` [PATCH v10 2/6] x86/sev: Initialize RMPOPT configuration MSRs Ashish Kalra
2026-06-30 18:11 ` [PATCH v10 3/6] x86/sev: Disable CPU hotplug while SNP is active Ashish Kalra
2026-07-01 9:40 ` Jethro Beekman
2026-07-01 16:39 ` K Prateek Nayak [this message]
2026-07-01 21:08 ` Kalra, Ashish
2026-07-01 21:25 ` Kalra, Ashish
2026-06-30 18:11 ` [PATCH v10 4/6] x86/sev: Add support to perform RMP optimizations asynchronously Ashish Kalra
2026-06-30 18:11 ` [PATCH v10 5/6] x86/sev: Add interface to re-enable RMP optimizations Ashish Kalra
2026-06-30 18:12 ` [PATCH v10 6/6] KVM: SEV: Perform RMP optimizations on SNP guest shutdown Ashish Kalra
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