Re: [Xen-devel] [PATCH v12 for-xen-4.5 11/20] x86/VPMU: Interface for setting PMU mode and flags

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/25/2014 03:28 PM, Boris Ostrovsky wrote:
> Add runtime interface for setting PMU mode and flags. Three main modes are
> provided:
> * XENPMU_MODE_OFF:  PMU is not virtualized
> * XENPMU_MODE_SELF: Guests can access PMU MSRs and receive PMU interrupts.
> * XENPMU_MODE_HV: Same as XENPMU_MODE_SELF for non-proviledged guests, dom0
>    can profile itself and the hypervisor.
>
> Note that PMU modes are different from what can be provided at Xen's boot line
> with 'vpmu' argument. An 'off' (or '0') value is equivalent to XENPMU_MODE_OFF.
> Any other value, on the other hand, will cause VPMU mode to be set to
> XENPMU_MODE_SELF during boot.
>
> For feature flags only Intel's BTS is currently supported.
>
> Mode and flags are set via HYPERVISOR_xenpmu_op hypercall.
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Do you think it would be useful for some service domain in a disaggregated
system to be able to query but not modify these PMU settings (i.e. only use
XENPMU_mode_get and XENPMU_feature_get)?  If this might be useful, then
splitting up the permission checks to use two bits (pmu_get, pmu_set) is
preferred.  However, I don't want to suggest this split if it will never be
useful - and I think that's the case here.  If you agree, then:

Acked-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

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