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Re: [Xen-devel] [PATCH v17 00/23] x86/PMU: Xen PMU PV(H) support

On 01/20/2015 05:37 AM, Jan Beulich wrote:
On 05.01.15 at 22:43, <boris.ostrovsky@xxxxxxxxxx> wrote:
Changes in v17:
* Disable VPMU when unknown CPU vendor is detected (patch #2)
* Remove unnecessary vendor tests in vendor-specific init routines (patch #14)
* Remember first CPU that starts mode change and use it to stop the cycle 
(patch #13)
* If vpmu ops is not present, return 0 as value for VPMU MSR read (as opposed to
   returning an error as was the case in previous patch.) (patch #18)
Any particular reason for this?

PVH guests access MSR_IA32_MISC_ENABLE early during boot, before VPMU initialization code had a chance to run and set vpmu ops. Returning 1 from vpmu_do_msr() would result in a fatal fault.

(This change would also be consistent with what core2_no_vpmu_ops does.)

I should have explained this in the cover letter.


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