Re: [RFC PATCH for-4.22 1/2] x86/platform: Expose DTS sensors MSR

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.10.2025 20:38, Andrew Cooper wrote:
> On 27/10/2025 5:26 pm, Teddy Astie wrote:
>> I'm not a fan of doing a inline cpuid check here, but I don't have a
>> better approach in mind.
> 
> I'm not sure if there's enough information in leaf 6 to justify putting
> it fully into the CPUID infrastructure.
> 
> But, if you do something like this:
> 
> diff --git a/xen/include/xen/lib/x86/cpu-policy.h 
> b/xen/include/xen/lib/x86/cpu-policy.h
> index f94f23e159d2..d02fe4d22151 100644
> --- a/xen/include/xen/lib/x86/cpu-policy.h
> +++ b/xen/include/xen/lib/x86/cpu-policy.h
> @@ -121,7 +121,13 @@ struct cpu_policy
>              uint64_t :64, :64; /* Leaf 0x3 - PSN. */
>              uint64_t :64, :64; /* Leaf 0x4 - Structured Cache. */
>              uint64_t :64, :64; /* Leaf 0x5 - MONITOR. */
> -            uint64_t :64, :64; /* Leaf 0x6 - Therm/Perf. */
> +
> +            /* Leaf 0x6 - Thermal and Perf. */
> +            struct {
> +                bool /* a */ dts:1;
> +                uint32_t /* b */:32, /* c */:32, /* d */:32;
> +            };
> +
>              uint64_t :64, :64; /* Leaf 0x7 - Structured Features. */
>              uint64_t :64, :64; /* Leaf 0x8 - rsvd */
>              uint64_t :64, :64; /* Leaf 0x9 - DCA */

Just to mention, below a patch I have pending as part of a series to
e.g. replace the various CPUID6_* values we presently use. As you did
indicate when we talked about this, a prereq to then use respective
bits from host_policy is an adjustment to cpu-policy.c, which is also
part of that series. If we weren't in freeze right now, I would have
posted the series already.

Jan

x86/cpu-policy: define bits of leaf 6

... as far as we presently use them in the codebase.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Or should we make both parts proper featureset elements? At least
APERFMPERF could likely be made visible to guests (in principle).

--- a/xen/include/xen/lib/x86/cpu-policy.h
+++ b/xen/include/xen/lib/x86/cpu-policy.h
@@ -128,7 +128,31 @@ struct cpu_policy
             uint64_t :64, :64; /* Leaf 0x3 - PSN. */
             uint64_t :64, :64; /* Leaf 0x4 - Structured Cache. */
             uint64_t :64, :64; /* Leaf 0x5 - MONITOR. */
-            uint64_t :64, :64; /* Leaf 0x6 - Therm/Perf. */
+
+            /* Leaf 0x6 - Therm/Perf. */
+            struct {
+                uint32_t /* a */:1,
+                    turbo:1,
+                    arat:1,
+                    :4,
+                    hwp:1,
+                    hwp_notification:1,
+                    hwp_activity_window:1,
+                    hwp_epp:1,
+                    hwp_plr:1,
+                    :1,
+                    hdc:1,
+                    :2,
+                    hwp_peci:1,
+                    :2,
+                    hw_feedback:1,
+                    :12;
+                uint32_t /* b */:32;
+                uint32_t /* c */ aperfmperf:1,
+                    :31;
+                uint32_t /* d */:32;
+            } pm;
+
             uint64_t :64, :64; /* Leaf 0x7 - Structured Features. */
             uint64_t :64, :64; /* Leaf 0x8 - rsvd */
             uint64_t :64, :64; /* Leaf 0x9 - DCA */