From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Jon Kohler <jon@nutanix.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Brian Gerst <brgerst@gmail.com>,
Brendan Jackman <jackmanb@google.com>,
"Ahmed S. Darwish" <darwi@linutronix.de>,
Alexandre Chartre <alexandre.chartre@oracle.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/its: use Sapphire Rapids+ feature to opt out
Date: Mon, 20 Oct 2025 12:44:54 -0700 [thread overview]
Message-ID: <20251020194446.w2s5f6nr7i7vw4ve@desk> (raw)
In-Reply-To: <20251017011253.2937710-1-jon@nutanix.com>
On Thu, Oct 16, 2025 at 06:12:49PM -0700, Jon Kohler wrote:
> A VMM may not expose ITS_NO or BHI_CTL, so guests cannot rely on those
> bits to determine whether they might be migrated to ITS-affected
> hardware. Rather than depending on a control that may be absent, detect
> ITS-unaffected hosts via a CPU feature that is exclusive to Sapphire
> Rapids and newer processors.
BHI_CTRL is also exclusive to Sapphire Rapids and newer processors. Why
wouldn't it be exposed to guests but BUS_LOCK_DETECT would be?
Not exposing BHI_CTRL has another disadvantage that guests would deploy the
BHB-clear sequence when they could have used cheaper hardware mitigation
for BHI.
> Use X86_FEATURE_BUS_LOCK_DETECT as the canary: it is present on
> Sapphire Rapids+ parts and provides a reliable indicator that the guest
> won't be moved to ITS-affected hardware.
I am puzzled why BUS_LOCK_DETECT is more reliable than BHI_CTRL?
next prev parent reply other threads:[~2025-10-20 19:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-17 1:12 Jon Kohler
2025-10-20 15:48 ` Sean Christopherson
2025-10-20 16:05 ` Jon Kohler
2025-10-20 16:21 ` Dave Hansen
2025-10-20 16:26 ` Jon Kohler
2025-10-20 19:26 ` Pawan Gupta
2025-10-20 19:38 ` Jon Kohler
2025-10-20 19:53 ` Pawan Gupta
2025-10-20 20:29 ` Jon Kohler
2025-10-20 19:44 ` Pawan Gupta [this message]
2025-10-20 19:54 ` Jon Kohler
2025-10-20 20:40 ` Pawan Gupta
2025-10-20 21:02 ` Jon Kohler
2025-10-20 22:09 ` Dave Hansen
2025-10-20 22:41 ` Pawan Gupta
2025-10-21 13:40 ` Jon Kohler
2025-10-21 14:01 ` Dave Hansen
2025-10-21 14:39 ` Jon Kohler
2025-10-21 15:21 ` Dave Hansen
2025-10-21 15:40 ` Jon Kohler
2025-10-21 15:27 ` Konrad Rzeszutek Wilk
2025-10-21 15:35 ` Jon Kohler
2025-10-21 15:46 ` Konrad Rzeszutek Wilk
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