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RE: [PATCH v5 06/18] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: "Penny, Zheng" <penny.zheng@xxxxxxx>
- Date: Thu, 19 Jun 2025 08:43:59 +0000
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- Cc: "Huang, Ray" <Ray.Huang@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, "Orzel, Michal" <Michal.Orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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- Thread-topic: [PATCH v5 06/18] xen/x86: introduce "cpufreq=amd-cppc" xen cmdline
[Public]
> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Thursday, June 12, 2025 6:42 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Anthony PERARD <anthony.perard@xxxxxxxxxx>;
> Orzel, Michal <Michal.Orzel@xxxxxxx>; Julien Grall <julien@xxxxxxx>; Roger Pau
> Monné <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 06/18] xen/x86: introduce "cpufreq=amd-cppc" xen
> cmdline
>
> On 27.05.2025 10:48, Penny Zheng wrote:
> > --- a/xen/arch/x86/platform_hypercall.c
> > +++ b/xen/arch/x86/platform_hypercall.c
> > @@ -94,6 +95,8 @@ static int __init handle_cpufreq_cmdline(enum
> > cpufreq_xen_opt option) {
> > int ret = 0;
> >
> > + /* Do not occupy bits reserved for public xen-pm */
> > + BUILD_BUG_ON(MASK_INSR(XEN_PROCESSOR_PM_CPPC,
> SIF_PM_MASK));
>
> This looks like an abuse of MASK_INSR(). Why not simply
>
> BUILD_BUG_ON(XEN_PROCESSOR_PM_CPPC & SIF_PM_MASK);
>
> ?
Because in SIF_PM_MASK, it's bit 8 to 15 reserved for xen-pm options,
See "
#define SIF_PM_MASK (0xFF<<8) /* reserve 1 byte for xen-pm options */
"
So I'm trying to use MASK_INSR() to do the necessary right shift (other than
using 8 directly, in case SIF_PM_MASK changes in the future...)
>
> Jan
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