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

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Message-ID: <0cdc6e9d-88eb-4ead-8d55-985474257d53@suse.com>
Date: Thu, 24 Apr 2025 10:14:20 +0200
From: Jürgen Groß <jgross@...e.com>
To: Xin Li <xin@...or.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism
 to write MSR

On 24.04.25 10:06, Xin Li wrote:
> On 4/23/2025 9:05 AM, 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().
>>
>> The case of the new immediate form could be handled the same way.
> 
> Actually, that is how we get this patch with the existing alternatives
> infrastructure.  And we took a step further to also remove the pv_ops
> MSR APIs...

And this is what I'm questioning. IMHO this approach is adding more
code by removing the pv_ops MSR_APIs just because "pv_ops is bad". And
I believe most refusal of pv_ops is based on no longer valid reasoning.

> It looks to me that you want to add a new facility to the alternatives
> infrastructure first?

Why would we need a new facility in the alternatives infrastructure?


Juergen

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