From: Marc Zyngier <firstname.lastname@example.org> To: email@example.com, firstname.lastname@example.org, email@example.com Cc: James Morse <firstname.lastname@example.org>, Julien Thierry <email@example.com>, Suzuki K Poulose <firstname.lastname@example.org>, Robin Murphy <Robin.Murphy@arm.com> Subject: Re: [PATCH 0/2] KVM: arm64: Filtering PMU events Date: Sat, 15 Feb 2020 13:00:55 +0000 Message-ID: <20200215130055.0995efe7@why> (raw) In-Reply-To: <email@example.com> On Fri, 14 Feb 2020 18:36:13 +0000 Marc Zyngier <firstname.lastname@example.org> wrote: > It is at times necessary to prevent a guest from being able to sample > certain events if multiple CPUs share resources such as a cache level. > In this case, it would be interesting if the VMM could simply prevent > certain events from being counted instead of simply not exposing a PMU. > > Given that most events are not architected, there is no easy way > to designate which events shouldn't be counted other than specifying > the raw event number. > > Since I have no idea whether it is better to use an event whitelist > or blacklist, the proposed API takes a cue from the x86 version and > allows either allowing or denying counting of ranges of events. > The event space being pretty large (16bits on ARMv8.1), the default > policy is set by the first filter that gets installed (default deny if > we first allow, default allow if we first deny). > > The filter state is global to the guest, despite the PMU being per > CPU. I'm not sure whether it would be worth it making it CPU-private. > > Anyway, I'd be interesting in comments on how people would use this. > I'll try to push a patch against kvmtool that implement this shortly > (what I have currently is a harcoded set of hacks). I now have a small extension to kvmtool allowing a --pmu-filter option to be passed on the command line (see ). I've also pushed out an update to the kernel side of things, making the filtering of the cycle counter consistent and documenting that neither SW_INCR nor CHAIN could be filtered with this mechanism (but this is of course up for discussion). Thanks, M.  https://git.kernel.org/pub/scm/linux/kernel/git/maz/kvmtool.git/commit/?h=pmu-filter  https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/pmu-event-filter -- Jazz is not dead. It just smells funny...
prev parent reply index Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-14 18:36 Marc Zyngier 2020-02-14 18:36 ` [PATCH 1/2] KVM: arm64: Add PMU event filtering infrastructure Marc Zyngier 2020-02-14 22:01 ` Robin Murphy 2020-02-15 10:28 ` Marc Zyngier 2020-02-17 15:33 ` Robin Murphy 2020-02-14 18:36 ` [PATCH 2/2] KVM: arm64: Document PMU filtering API Marc Zyngier 2020-02-15 13:00 ` Marc Zyngier [this message]
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