On Wed, Jul 11, 2018 at 06:59:28AM +0100, Mark Rutland wrote: > On Mon, Jul 09, 2018 at 06:42:29PM -0400, Boris Ostrovsky wrote: > > On 07/02/2018 12:02 PM, Mark Rutland wrote: > > > On Mon, Jul 02, 2018 at 05:46:55PM +0200, Peter Zijlstra wrote: > > >> On Mon, Jul 02, 2018 at 04:12:50PM +0100, Mark Rutland wrote: > > >>> +static struct pt_regs *perf_get_sample_regs(struct perf_event *event, > > >>> + struct pt_regs *regs) > > >>> +{ > > >>> + /* > > >>> + * Due to interrupt latency (AKA "skid"), we may enter the > > >>> kernel > > >>> + * before taking an overflow, even if the PMU is only counting > > >>> user > > >>> + * events. > > >>> + * > > >>> + * If we're not counting kernel events, always use the user > > >>> regs when > > >>> + * sampling. > > >>> + * > > >>> + * TODO: what do we do about sampling a guest's registers? The > > >>> IP is > > >>> + * special-cased, but for the rest of the regs they'll get the > > >>> + * user/kernel regs depending on whether exclude_kernel is set, > > >>> which > > >>> + * is nonsensical. > > >>> + * > > >>> + * We can't get at the full set of regs in all cases (e.g. > > >>> Xen's PV PMU > > >>> + * can't provide the GPRs), so should we just zero the GPRs > > >>> when in a > > >>> + * guest? Or skip outputting the regs in perf_output_sample? > > >> Seems daft Xen cannot provide registers; why is that? Boris? > > > The xen_pmu_regs structure simply doesn't have them, so I assume there's > > > no API to get them. > > > > > > Given we don't currently sample the guest regs, I'd be tempted to just > > > zero them for now, or skip the sample at output time (if that doesn't > > > break some other case).
> I think this is going to become a series rather than a single patch, but I can > have a go. I need to get my head around how the various cases interact with > each other. As a heads-up, due to sabbatical leave I'm probably not going to have the chance to dig into this until September. If someone else is able to take a look at this, that would be great. Otherwise, I'm happy to take a look once I get back. Thanks, Mark.