Messages in this thread | | | Subject | Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples | From | Like Xu <> | Date | Wed, 12 Aug 2020 15:25:03 +0800 |
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On 2020/8/12 11:52, Jin, Yao wrote: > Hi Peter, > > On 8/11/2020 4:45 PM, Peter Zijlstra wrote: >> On Tue, Aug 11, 2020 at 04:31:10PM +0800, Jin, Yao wrote: >>> Hi Peter, >>> >>> On 8/11/2020 3:59 PM, Peter Zijlstra wrote: >>>> On Tue, Aug 11, 2020 at 03:50:43PM +0800, Jin, Yao wrote: >>>>> Could I post v2 which basically refers to your patch but removes some >>>>> conditions since I see some issues in test if we use these conditions. >>>>> >>>>> 1. Remove '!event->attr.exclude_hv || !event->attr.exclude_host || >>>>> !event->attr.exclude_guest' at the entry of sanitize_sample_regs(). >>>>> >>>>> 2. Remove '!attr.exclude_hv || !attr.exclude_host || >>>>> !attr.exclude_guest' >>>>> at the perf_event_open syscall entry. >>>> >>>> exclude_host, maybe -- due to the dodgy semantics of it, but the others >>>> should definitely be there. >>>> >>> >>> exclude_guest and exclude_hv are tricky too. >>> >>> If we do 'perf record -e cycles:u' in both host and guest, we can see: >>> >>> event->attr.exclude_guest = 0 >>> >>> thus sanitize_sample_regs() returns regs directly even if exclude_kernel >>> = 1. >>> >>> And in guest, exclude_hv = 0, it's out of my expectation too. >> >> I'm confused, how can 'perf record -e cycles:u' _ever_ have >> exclude_guest=0, exclude_hv=0 ? That simply makes no sense and is utterly >> broken. >> >> You explicitly ask for userspace-only, reporting hypervisor or guest >> events is a straight up bug.
Guest events = guest user-space events + guest kernel-space events.
Some perf users on the host may only want to count guest user space events.
>> > > If we run 'perf record -e cycles:u', > > 1. On host, exclude_guest = 0 and exclude_hv = 1 > > perf tool doesn't specially set 'exclude_guest' when it parses the 'u' > modifier. I agree that can be improved. I will post a perf tool patch to > fix that. > > 2. On guest, exclude_guest = 0 and exclude_hv = 0. > > For exclude_hv = 0, it looks like a bug but x86 doesn't use exclude_hv. But > yes, we should fix that. > > CC Like Xu <like.xu@linux.intel.com>. > > Thanks > Jin Yao
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