From: Ionela Voinescu <ionela.voinescu@arm.com> To: Valentin Schneider <valentin.schneider@arm.com> Cc: Suzuki Kuruppassery Poulose <suzuki.poulose@arm.com>, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, maz@kernel.org, sudeep.holla@arm.com, dietmar.eggemann@arm.com, peterz@infradead.org, mingo@redhat.com, ggherdovich@suse.cz, vincent.guittot@linaro.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry.kdev@gmail.com> Subject: Re: [PATCH v2 3/6] arm64/kvm: disable access to AMU registers from kvm guests Date: Tue, 28 Jan 2020 17:52:23 +0000 [thread overview] Message-ID: <20200128175223.GA31241@arm.com> (raw) In-Reply-To: <5de3d3c7-2d78-9d18-f3ca-7cb6cf9ce36c@arm.com> On Tuesday 28 Jan 2020 at 17:37:04 (+0000), Valentin Schneider wrote: > Hi Suzuki, > > On 28/01/2020 17:26, Suzuki Kuruppassery Poulose wrote: > >> So, providing I didn't get completely lost on the way, I have to ask: > >> why do we use CPACR_EL1 here? Couldn't we use CPTR_EL2 directly? > > > > Part of the reason is, CPTR_EL2 has different layout depending on > > whether HCR_EL2.E2H == 1. e.g, CPTR_EL2.TTA move from Bit[28] to Bit[20]. > > > > So, to keep it simple, CPTR_EL2 is used for non-VHE code with the shifts > > as defined by the "CPTR_EL2 when E2H=0" > > > > if E2H == 1, CPTR_EL2 takes the layout of CPACR_EL1 and "overrides" some > > of the RES0 bits in CPACR_EL1 with EL2 controls (e.g: TAM, TCPAC). > > Thus we use CPACR_EL1 to keep the "shifts" non-conflicting (e.g, ZEN) > > and is the right thing to do. > > > > It is a bit confusing, but we are doing the right thing. May be we could improve the comment like : > > > > /* > > * With VHE (HCR.E2H == 1), CPTR_EL2 has the same layout as > > * CPACR_EL1, except for some missing controls, such as TAM. > > * And accesses to CPACR_EL1 are routed to CPTR_EL2. > > * Also CPTR_EL2.TAM has the same position with or without > > * HCR.E2H == 1. Therefore, use CPTR_EL2.TAM here for > > * trapping the AMU accesses. > > */ > > Thanks Suzuki, this makes sense! Ionela. > > Thanks for clearing this up! I also bothered MarcZ in the meantime who > also cleared up some of my confusion (including which layout takes effect). > > So yeah, I think what we want here is to keep using CPTR_EL2_TAM but have a > comment that explains why (which you just provided!). > > > Suzuki
next prev parent reply other threads:[~2020-01-28 17:52 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-12-18 18:26 [PATCH v2 0/6] arm64: ARMv8.4 Activity Monitors support Ionela Voinescu 2019-12-18 18:26 ` [PATCH v2 1/6] arm64: add support for the AMU extension v1 Ionela Voinescu 2020-01-23 17:04 ` Valentin Schneider 2020-01-23 18:32 ` Ionela Voinescu 2020-01-24 12:00 ` Valentin Schneider 2020-01-28 11:00 ` Ionela Voinescu 2020-01-28 16:34 ` Suzuki Kuruppassery Poulose 2020-01-29 16:42 ` Ionela Voinescu 2019-12-18 18:26 ` [PATCH v2 2/6] arm64: trap to EL1 accesses to AMU counters from EL0 Ionela Voinescu 2020-01-23 17:04 ` Valentin Schneider 2020-01-23 17:34 ` Ionela Voinescu 2019-12-18 18:26 ` [PATCH v2 3/6] arm64/kvm: disable access to AMU registers from kvm guests Ionela Voinescu 2020-01-27 15:33 ` Valentin Schneider 2020-01-28 15:48 ` Ionela Voinescu 2020-01-28 17:26 ` Suzuki Kuruppassery Poulose 2020-01-28 17:37 ` Valentin Schneider 2020-01-28 17:52 ` Ionela Voinescu [this message] 2019-12-18 18:26 ` [PATCH v2 4/6] Documentation: arm64: document support for the AMU extension Ionela Voinescu 2020-01-27 16:47 ` Valentin Schneider 2020-01-28 16:53 ` Ionela Voinescu 2020-01-28 18:36 ` Valentin Schneider 2020-01-30 15:04 ` Suzuki Kuruppassery Poulose 2020-01-30 16:45 ` Ionela Voinescu 2020-01-30 18:26 ` Suzuki K Poulose 2020-01-31 9:54 ` Ionela Voinescu 2019-12-18 18:26 ` [PATCH v2 5/6] TEMP: sched: add interface for counter-based frequency invariance Ionela Voinescu 2020-01-29 19:37 ` Peter Zijlstra 2020-01-30 15:33 ` Ionela Voinescu 2019-12-18 18:26 ` [PATCH v2 6/6] arm64: use activity monitors for " Ionela Voinescu 2020-01-23 11:49 ` Lukasz Luba 2020-01-23 17:07 ` Ionela Voinescu 2020-01-24 1:19 ` Lukasz Luba 2020-01-24 13:12 ` Ionela Voinescu 2020-01-24 15:17 ` Lukasz Luba 2020-01-28 17:36 ` Ionela Voinescu 2020-01-29 17:13 ` Valentin Schneider 2020-01-29 17:52 ` Ionela Voinescu 2020-01-29 23:39 ` Valentin Schneider 2020-01-30 15:49 ` Ionela Voinescu 2020-01-30 16:11 ` Valentin Schneider
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