Re: [PATCH v5 2/7] x86/msr: add wrmsrq_on_cpus helper

[Borislav Petkov]

On Thu, May 28, 2026 at 02:55:44PM -0500, Kalra, Ashish wrote:
> Hello Dave,
> 
> On 5/28/2026 2:50 PM, Dave Hansen wrote:
> > On 5/28/26 12:37, Kalra, Ashish wrote:
> >> A simple loop would be perfectly fine and avoids the need for the wrmsrq_on_cpus() helper entirely:
> >>
> >>   for_each_cpu(cpu, &rmpopt_cpumask)
> >>       wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE, rmpopt_base);
> > 
> > I'm glad we're on the same page finally. I just hope we can get to this
> > point more quickly next time. I started off with exactly this
> > suggestion, but someone chimed in to the thread and said it was "slower":
> > 
> >> https://lore.kernel.org/lkml/6a50d050-f602-43fd-a44a-cecedd9823eb@xxxxxxx/
> > 
> 
> Yes, actually i should have made it explicitly clear that we need to do it in
> parallel especially for issuing the RMPOPT instruction itself, as that is
> in a performance critical path (and for that we are using on_each_cpu_mask()).

So which is it? Do we need the wrmsrq_on_cpus() helper or not?

I'm confused.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette