On 11/23/2015 05:01 PM, Brendan Gregg wrote:
On Mon, Nov 23, 2015 at 6:35 AM, Boris Ostrovsky
<boris.ostrov...@oracle.com <mailto:boris.ostrov...@oracle.com>> wrote:
On 11/20/2015 07:21 PM, Brendan Gregg wrote:
These new features would need a corresponding change in Linux for
PV guests (or for dom0 to change feature set globally). But before
that do_xenpmu_op()'s XENPMU_feature_set clause will have to be
updated to deal with new modes.
Ok, thanks. For now this is HVM, and I can EINVAL in do_xenpmu_op()
for the new modes, like with BTS. (Do you know if the later Linux
changes would be more than a feature version of
pmu_mode_store/pmu_mode_show?)
You are right --- Linux doesn't need anything, it just passes the
features directly to the hypervisor. pmu_mode_store/show convert strings
to numbers but we don't use strings for features.
So the only thing that's needed is to allow hypervisor set/clear those
two bits in vpmu_features in do_xenpmu_op().
Also, if either of those two flags is set we probably want to
block MSR_IA32_DS_AREA and MSR_IA32_PEBS_ENABLE accesses as well.
Ok, yes, good idea.
But: DS area is needed by BTS so if that feature is set we want to allow
guests to write it (and as for PEBS (which also uses DS area) --- that's
really a nop so whether or not you block it won't make any difference.
But we should probably still do it).
I don't know whether anyone else uses debug store. The way SDM's section
18.11.4 describes it there doesn't seem to be any other users.
-boris
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