Re: [RFC PATCH for-4.22 v2 1/3] x86/cpu-policy: Infrastructure for CPUID leaf 0x6

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.10.2025 16:59, Teddy Astie wrote:
> From: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
> ---
> v2: introduced

This being a change of mine, I'm not happy for the title to have changed, and
for the (little bit of) description to have been dropped.

> --- a/xen/include/xen/lib/x86/cpu-policy.h
> +++ b/xen/include/xen/lib/x86/cpu-policy.h
> @@ -121,7 +121,32 @@ 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 */
> +                    dts: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 */

As I had said, this (really: the use of these bits in the host policy) actually
requires an adjustment to cpu-policy.c as well, which I'm carrying as a 
separate,
prereq change (re-produced below). May I suggest that your work go on top of 
mine
(which I'll post once we have branched 4.21 off)?

Jan

x86/cpu-policy: move invocation of recalculate_misc()

The function is about guest exposure of features / leaves. There's no need
for it to be applied on the host policy. In fact doing so gets in the way
of using the host policy in certain places.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -424,7 +424,6 @@ void __init calculate_host_policy(void)
     x86_cpu_featureset_to_policy(boot_cpu_data.x86_capability, p);
     recalculate_xstate(p);
     recalculate_tile(p);
-    recalculate_misc(p);
 
     /* When vPMU is disabled, drop it from the host policy. */
     if ( vpmu_mode == XENPMU_MODE_OFF )
@@ -705,6 +704,7 @@ static void __init calculate_pv_max_poli
     unsigned int i;
 
     *p = host_cpu_policy;
+    recalculate_misc(p);
 
     guest_common_max_leaves(p);
 
@@ -809,6 +809,7 @@ static void __init calculate_hvm_max_pol
     const uint32_t *mask;
 
     *p = host_cpu_policy;
+    recalculate_misc(p);
 
     guest_common_max_leaves(p);