linux-kernel - RE: [PATCH] x86: also disable FSRM if ERMS is disabled

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Message-ID: <SJ1PR11MB60835F7CF6645527DDC63713FC239@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Tue, 11 Oct 2022 22:19:12 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Daniel Verkamp <dverkamp@...omium.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: RE: [PATCH] x86: also disable FSRM if ERMS is disabled

> That won't help because userspace will still use them since the CPUID
> flags remain set.

Even if writing the MSR did clear the CPUID bits, it wouldn't help with applications
that started before the kernel cleared the bits (assuming this was some run-time
update patch).

Worst case scenario is that the applications don't pick the most efficient memcpy().

-Tony