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

On 09/25/2014 03:28 PM, Boris Ostrovsky wrote:
Add runtime interface for setting PMU mode and flags. Three main modes are
* 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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