linux-kernel - Re: [PATCH v1 2/4] x86/fred: Write to FRED MSRs with wrmsrns()

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Message-ID: <dc1b2c50-6172-46a1-98a8-cec729afff38@intel.com>
Date: Wed, 3 Jul 2024 09:43:05 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "H. Peter Anvin" <hpa@...or.com>,
 Andrew Cooper <andrew.cooper3@...rix.com>, Borislav Petkov <bp@...en8.de>
Cc: xin@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
 mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
 peterz@...radead.org, nik.borisov@...e.com, houwenlong.hwl@...group.com
Subject: Re: [PATCH v1 2/4] x86/fred: Write to FRED MSRs with wrmsrns()

On 7/3/24 09:06, H. Peter Anvin wrote:
> I believe tglx declared to use them unconditionally since FRED> depends on WRMSRNS (and the kernel enforces that.)

Ahh, I forgot about:

static const struct cpuid_dep cpuid_deps[] = {
	...
        { X86_FEATURE_FRED,                     X86_FEATURE_WRMSRNS   },

So, yeah, Xin's patch here is quite safe and when Boris said:

> Also, all those wrmsrns() writes better be behind a CPUID check.

... it *is* behind a CPUID check, but it's an implicit one.