Messages in this thread | | | Subject | Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples | From | "Jin, Yao" <> | Date | Wed, 12 Aug 2020 11:52:43 +0800 |
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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. >
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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