linux-kernel - Re: [PATCH] x86/its: use Sapphire Rapids+ feature to opt out

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Message-ID: <67cdba64-d1e7-4f18-b790-4ecd2c573bb0@intel.com>
Date: Tue, 21 Oct 2025 08:21:54 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jon Kohler <jon@...anix.com>
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org"
 <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Brian Gerst <brgerst@...il.com>, Brendan Jackman <jackmanb@...gle.com>,
 "Ahmed S. Darwish" <darwi@...utronix.de>,
 Alexandre Chartre <alexandre.chartre@...cle.com>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/its: use Sapphire Rapids+ feature to opt out

On 10/21/25 07:39, Jon Kohler wrote:
> For BHI_CTRL, depending on what QEMU the VM was originally *started* on,
> the guest may have access to Sapphire Rapids models, but BHI_CTRL may
> not have existed in the QEMU source at that time, as those were introduced
> into two different timeframes.

I have two solutions for you here, and neither of them involves patching
the kernel.

First, I personally volunteer to travel to your customers' homes to
provide in-person education with my "education stick" about why updating
software is important.

Second, if they continue to be education-resistant, I offer to
personally travel to the datacenters where these VMs are running to
inspect the racks where they run and brainstorm solutions. A warning,
though: I am quite clumsy and I've been known to bump into power cables
and circuit breakers.