linux-kernel - Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism to write MSR

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Message-ID: <35979102-2eb2-4566-b32a-f2b02ded8ae6@suse.com>
Date: Fri, 25 Apr 2025 14:51:27 +0200
From: Jürgen Groß <jgross@...e.com>
To: Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism
 to write MSR

On 25.04.25 14:33, Peter Zijlstra wrote:
> On Wed, Apr 23, 2025 at 06:05:19PM +0200, Jürgen Groß wrote:
> 
>>> It's not a major change, but when it is patched to use the immediate
>>> form MSR write instruction, it's straightforwardly streamlined.
>>
>> It should be rather easy to switch the current wrmsr/rdmsr paravirt patching
>> locations to use the rdmsr/wrmsr instructions instead of doing a call to
>> native_*msr().
> 
> Right, just make the Xen functions asm stubs that expect the instruction
> registers instead of C-abi and ALT_NOT_XEN the thing.
> 
> Shouldn't be hard at all.

Correct. And for the new immediate form we can use ALTERNATIVE_3().


Juergen

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