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Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism to write MSR
- To: Jürgen Groß <jgross@xxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Fri, 25 Apr 2025 13:12:33 -0700
- Cc: Xin Li <xin@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-perf-users@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-pm@xxxxxxxxxxxxxxx, linux-edac@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-acpi@xxxxxxxxxxxxxxx, linux-hwmon@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, platform-driver-x86@xxxxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, mingo@xxxxxxxxxx, bp@xxxxxxxxx, dave.hansen@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, acme@xxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, namhyung@xxxxxxxxxx, mark.rutland@xxxxxxx, alexander.shishkin@xxxxxxxxxxxxxxx, jolsa@xxxxxxxxxx, irogers@xxxxxxxxxx, adrian.hunter@xxxxxxxxx, kan.liang@xxxxxxxxxxxxxxx, wei.liu@xxxxxxxxxx, ajay.kaher@xxxxxxxxxxxx, bcm-kernel-feedback-list@xxxxxxxxxxxx, tony.luck@xxxxxxxxx, pbonzini@xxxxxxxxxx, vkuznets@xxxxxxxxxx, seanjc@xxxxxxxxxx, luto@xxxxxxxxxx, boris.ostrovsky@xxxxxxxxxx, kys@xxxxxxxxxxxxx, haiyangz@xxxxxxxxxxxxx, decui@xxxxxxxxxxxxx
- Delivery-date: Fri, 25 Apr 2025 20:13:25 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On April 25, 2025 5:51:27 AM PDT, "Jürgen Groß" <jgross@xxxxxxxx> wrote:
>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
Yes; in the ultimate case there are *four* alternatives, but the concept is the
same and again we have it implemented already.
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