From: K Prateek Nayak <kprateek.nayak@amd.com>
To: Borislav Petkov <bp@alien8.de>, "Kalra, Ashish" <ashish.kalra@amd.com>
Cc: <tglx@kernel.org>, <mingo@redhat.com>,
<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>, <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 v9 3/6] x86/sev: Disable CPU hotplug while SNP is active
Date: Mon, 29 Jun 2026 08:35:04 +0530 [thread overview]
Message-ID: <75a397c3-5251-45c8-8aba-a185685b382d@amd.com> (raw)
In-Reply-To: <20260627044117.GEaj9UbSvTExfmFilu@fat_crate.local>
Hello Boris,
On 6/27/2026 10:11 AM, Borislav Petkov wrote:
> You could also block hotplug for the time being by grabbing cpus_read_lock().
> And only when you know you are all clear to disable hotplug, then you can do
> that in the end and drop the hotplug lock.
This is bad idea because it'll stall the tasks trying to do a hotplug
until the last SNP VM exits. Instead of simply getting an -EBUSY, the
users will start seeing a hung task splats in dmesg.
Also, since the last VM has to re-enable hotplug, you'll need a
up_read_non_owner() variant for cpus_read_unlock() to unlock the rwsem
from a different thread compared to the one that locks.
I think cpu_hotplug_disable() is the correct way to go forward but if
you are not a fan of the global "snp_cpu_hotplug_disabled" flag, maybe
it can be turned into an indicator like "snp_initialized" in
"struct sev_device". Thoughts?
--
Thanks and Regards,
Prateek
next prev parent reply other threads:[~2026-06-29 3:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1782336473.git.ashish.kalra@amd.com>
2026-06-24 21:56 ` [PATCH v9 1/6] x86/cpufeatures: Add X86_FEATURE_RMPOPT feature flag Ashish Kalra
2026-06-24 21:56 ` [PATCH v9 2/6] x86/sev: Initialize RMPOPT configuration MSRs Ashish Kalra
2026-06-24 21:56 ` [PATCH v9 3/6] x86/sev: Disable CPU hotplug while SNP is active Ashish Kalra
2026-06-25 3:45 ` K Prateek Nayak
2026-06-25 5:38 ` Kalra, Ashish
2026-06-30 14:18 ` Tom Lendacky
2026-06-25 15:02 ` Borislav Petkov
2026-06-25 19:42 ` Kalra, Ashish
2026-06-25 22:16 ` K Prateek Nayak
2026-06-26 2:38 ` Kalra, Ashish
2026-06-26 4:01 ` K Prateek Nayak
2026-06-26 20:23 ` Kalra, Ashish
2026-06-26 16:40 ` Borislav Petkov
2026-06-26 20:59 ` Kalra, Ashish
2026-06-27 4:41 ` Borislav Petkov
2026-06-29 3:05 ` K Prateek Nayak [this message]
2026-06-29 3:11 ` Kalra, Ashish
2026-06-24 21:57 ` [PATCH v9 4/6] x86/sev: Add support to perform RMP optimizations asynchronously Ashish Kalra
2026-06-24 21:58 ` [PATCH v9 5/6] x86/sev: Add interface to re-enable RMP optimizations Ashish Kalra
2026-06-24 21:59 ` [PATCH v9 6/6] KVM: SEV: Perform RMP optimizations on SNP guest shutdown Ashish Kalra
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