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Re: [Xen-devel] [PATCH v13 for-xen-4.5 07/21] x86/VPMU: Handle APIC_LVTPC accesses

On 10/13/2014 09:02 AM, Jan Beulich wrote:
On 03.10.14 at 23:40, <boris.ostrovsky@xxxxxxxxxx> wrote:
@@ -706,10 +693,6 @@ static int core2_vpmu_do_interrupt(struct cpu_user_regs 
              return 0;
- /* HW sets the MASK bit when performance counter interrupt occurs*/
-    vpmu->hw_lapic_lvtpc = apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED;
-    apic_write_around(APIC_LVTPC, vpmu->hw_lapic_lvtpc);
So why is simply deleting this correct? The comment makes pretty
clear why it was being done here. All I could see being valid without
further explanation is the removal of the middle of the three lines.

It is expected that PMU interrupt will set the mask bit so whoever is using PMU hardware (bare-metal or virtualized) is expected to clear it. Therefore there is no reason for the hypervisor to do this.

I can add a note about it in the commit message.


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