Re: [Xen-devel] [PATCH] x86/vpmu: fix vpmu can't enabled in guest

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/17 02:19, Luwei Kang wrote:
> vpmu_enable() can not use for check if vpmu is enabled in guest during
> booting up. Because linux kernel get the status of if supported pmu
> is earler than xen vpmu initialise. vpmu_enable() will return false
> even if vpmu has been enabled in guest.

Sorry for breaking this.  However ...

> diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
> index e0a387e..b63c5d8 100644
> --- a/xen/arch/x86/cpuid.c
> +++ b/xen/arch/x86/cpuid.c
> @@ -713,8 +713,7 @@ static void pv_cpuid(uint32_t leaf, uint32_t subleaf, 
> struct cpuid_leaf *res)
>              }
>          }
>  
> -        if ( vpmu_enabled(curr) &&
> -             vpmu_is_set(vcpu_vpmu(curr), VPMU_CPU_HAS_DS) )
> +        if ( opt_vpmu_enabled && boot_cpu_has(X86_FEATURE_DS) )

... this is overly general.  The visibility of these flags must be per
domain, and not globally like this.

In particular, XENPMU_MODE_ALL needs to expose PMU to dom0, but hide it
from all other domains, while even in the XENPMU_MODE_SELF case, only
domains explicitly configured with PMU should see it (as it generally
unsafe to migrate with).

Longterm (with the inclusion of the CPUID improvements), my plan was to
have PMU available in the max policy but hidden in the default policy,
which requires the toolstack to explicitly opt in for domains.  It would
opt in/out by setting the version field in guests CPUID policy and the
other feature bits.

~Andrew

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