[v7] x86: Expose consistent topology to guests

[PATCH v7 01/10] lib/x86: Bump max basic leaf in {pv,hvm}_max_policy

Posted by Alejandro Vallejo 3 weeks, 2 days ago

Bump it to ARRAY_SIZE() so toolstack is able to extend a policy past
host limits (i.e: to emulate a feature not present in the host)

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
---
v7:
  * Replaces v6/patch1("Relax checks about policy compatibility")
  * Bumps basic.max_leaf to ARRAY_SIZE(basic.raw) to pass the
    compatibility checks rather than tweaking the checker.
---
 xen/arch/x86/cpu-policy.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index b6d9fad56773..715a66d2a978 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -585,6 +585,9 @@ static void __init calculate_pv_max_policy(void)
      */
     p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
 
+    /* Toolstack may populate leaves not present in the basic host leaves */
+    p->basic.max_leaf = ARRAY_SIZE(p->basic.raw) - 1;
+
     x86_cpu_policy_to_featureset(p, fs);
 
     for ( i = 0; i < ARRAY_SIZE(fs); ++i )
@@ -672,6 +675,9 @@ static void __init calculate_hvm_max_policy(void)
      */
     p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
 
+    /* Toolstack may populate leaves not present in the basic host leaves */
+    p->basic.max_leaf = ARRAY_SIZE(p->basic.raw) - 1;
+
     x86_cpu_policy_to_featureset(p, fs);
 
     mask = hvm_hap_supported() ?
-- 
2.47.0

Re: [PATCH v7 01/10] lib/x86: Bump max basic leaf in {pv,hvm}_max_policy

Posted by Andrew Cooper 2 weeks, 1 day ago

On 21/10/2024 4:45 pm, Alejandro Vallejo wrote:
> Bump it to ARRAY_SIZE() so toolstack is able to extend a policy past
> host limits (i.e: to emulate a feature not present in the host)
>
> Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
> ---
> v7:
>   * Replaces v6/patch1("Relax checks about policy compatibility")
>   * Bumps basic.max_leaf to ARRAY_SIZE(basic.raw) to pass the
>     compatibility checks rather than tweaking the checker.
> ---
>  xen/arch/x86/cpu-policy.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
> index b6d9fad56773..715a66d2a978 100644
> --- a/xen/arch/x86/cpu-policy.c
> +++ b/xen/arch/x86/cpu-policy.c
> @@ -585,6 +585,9 @@ static void __init calculate_pv_max_policy(void)
>       */
>      p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
>  
> +    /* Toolstack may populate leaves not present in the basic host leaves */
> +    p->basic.max_leaf = ARRAY_SIZE(p->basic.raw) - 1;
> +
>      x86_cpu_policy_to_featureset(p, fs);
>  
>      for ( i = 0; i < ARRAY_SIZE(fs); ++i )
> @@ -672,6 +675,9 @@ static void __init calculate_hvm_max_policy(void)
>       */
>      p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
>  
> +    /* Toolstack may populate leaves not present in the basic host leaves */
> +    p->basic.max_leaf = ARRAY_SIZE(p->basic.raw) - 1;
> +
>      x86_cpu_policy_to_featureset(p, fs);
>  
>      mask = hvm_hap_supported() ?

This sadly doesn't do what you want.  It leaves the default policy with
extended limits too.

To unblock the work (which is long overdue), here's one I prepared
earlie^W just now.

https://lore.kernel.org/xen-devel/20241029175505.2698661-1-andrew.cooper3@citrix.com/T/#u

~Andrew