linux-kernel - Re: [RFC PATCH v1 01/15] x86/msr: Replace __wrmsr() with native

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Message-ID: <03874E9B-FAEB-4ACA-B13D-0BED7D54F443@zytor.com>
Date: Mon, 31 Mar 2025 22:13:51 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Andrew Cooper <andrew.cooper3@...rix.com>,
        "Xin Li (Intel)" <xin@...or.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [RFC PATCH v1 01/15] x86/msr: Replace __wrmsr() with native_wrmsrl()

On March 31, 2025 2:45:43 PM PDT, Andrew Cooper <andrew.cooper3@...rix.com> wrote:
>On 31/03/2025 9:22 am, Xin Li (Intel) wrote:
>> __wrmsr() is the lowest level primitive MSR write API, and its direct
>> use is NOT preferred.  Use its wrapper function native_wrmsrl() instead.
>>
>> No functional change intended.
>>
>> Signed-off-by: Xin Li (Intel) <xin@...or.com>
>
>The critical piece of information you're missing from the commit message
>is that the MSR_IMM instructions take a single u64.
>
>Therefore to use them, you've got to arrange for all callers to provide
>a single u64, rather than a split u32 pair.
>
>~Andrew

That being said, there is nothing wrong with having a two-word convenience wrapper.