On 2021/1/16 1:42, Sean Christopherson wrote:
On Fri, Jan 15, 2021, Xu, Like wrote:
On 2021/1/15 2:55, Sean Christopherson wrote:
On Mon, Jan 04, 2021, Like Xu wrote:
+ * Note: KVM disables the co-existence of guest PEBS and host PEBS.
By "KVM", do you mean KVM's loading of the MSRs provided by intel_guest_get_msrs()?
Because the PMU should really be the entity that controls guest vs. host. KVM
should just be a dumb pipe that handles the mechanics of how values are context
switch.
The intel_guest_get_msrs() and atomic_switch_perf_msrs()
will work together to disable the co-existence of guest PEBS and host PEBS:
https://lore.kernel.org/kvm/961e6135-ff6d-86d1-3b7b-a1846ad0e4c4@xxxxxxxxx/
+
static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
...
if (nr_msrs > 2 && (msrs[1].guest & msrs[0].guest)) {
msrs[2].guest = pmu->ds_area;
if (nr_msrs > 3)
msrs[3].guest = pmu->pebs_data_cfg;
}
for (i = 0; i < nr_msrs; i++)
...
Yeah, that's exactly what I'm complaining about. Splitting the logic for
determining the guest values is unnecessarily confusing, and as evidenced by the
PEBS_ENABLE bug, potentially fragile. Perf should have full knowledge and
control of what values are loaded for the guest. And, the above indexing magic
is nigh impossible to follow and _super_ fragile.
Thanks for pointing this out.
If we change .guest_get_msrs() to take a struct kvm_pmu pointer, then it can
generate the full set of guest values by grabbing ds_area and pebs_data_cfg.
Alternatively, .guest_get_msrs() could take the desired guest MSR values
directly (ds_area and pebs_data_cfg), but kvm_pmu is vendor agnostic, so I don't
see any reason to not just pass the pointer.
Hi Peter,
What do you think of us passing a "struct kvm_pmu" pointer (defined in
arch/x86/include/asm/kvm_host.h) to guest_get_msrs(int *nr) ?
---
thx,likexu
