Messages in this thread | | | Date | Fri, 7 Aug 2020 11:02:32 +0200 | From | peterz@infradea ... | Subject | Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples |
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On Fri, Aug 07, 2020 at 02:24:30PM +0800, Jin, Yao wrote: > Hi Peter, > > On 8/6/2020 7:00 PM, peterz@infradead.org wrote: > > On Thu, Aug 06, 2020 at 11:18:27AM +0200, peterz@infradead.org wrote: > > > > > Suppose we have nested virt: > > > > > > L0-hv > > > | > > > G0/L1-hv > > > | > > > G1 > > > > > > And we're running in G0, then: > > > > > > - 'exclude_hv' would exclude L0 events > > > - 'exclude_host' would ... exclude L1-hv events? > > > - 'exclude_guest' would ... exclude G1 events? > > > > So in arch/x86/events/intel/core.c we have: > > > > static inline void intel_set_masks(struct perf_event *event, int idx) > > { > > struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > > > > if (event->attr.exclude_host) > > __set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_guest_mask); > > if (event->attr.exclude_guest) > > __set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_host_mask); > > if (event_is_checkpointed(event)) > > __set_bit(idx, (unsigned long *)&cpuc->intel_cp_status); > > } > > > > exclude_host is now set by guest (pmc_reprogram_counter, > arch/x86/kvm/pmu.c). When enabling the event, we can check exclude_host to > know if it's a guest. > > Otherwise we may need more flags in event->attr to indicate the status. > > > which is, afaict, just plain wrong. Should that not be something like: > > > > if (!event->attr.exclude_host) > > __set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_host_mask); > > if (!event->attr.exclude_guest) > > __set_bit(idx, (unsigned long *)&cpuc->intel_ctrl_guest_mask); > > > > > > How can we know it's guest or host even if exclude_host is set in guest?
I'm not following you, consider:
xh xg h g h' g' 0 0 0 0 1 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 1 1 0 0
So the 0,0 and 1,1 cases get flipped. I have a suspicion, but this _really_ should have fat comments all over :-(
What a sodding trainwreck..
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