From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, will@kernel.org,
catalin.marinas@arm.com, mark.rutland@arm.com,
James Clark <james.clark@arm.com>, Rob Herring <robh@kernel.org>,
Marc Zyngier <maz@kernel.org>,
Suzuki Poulose <suzuki.poulose@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-perf-users@vger.kernel.org
Subject: Re: [PATCH V9 00/10] arm64/perf: Enable branch stack sampling
Date: Fri, 24 Mar 2023 08:50:32 +0530 [thread overview]
Message-ID: <4665d03f-b801-679c-0b52-c426404284b9@arm.com> (raw)
In-Reply-To: <4d93a3de-c86d-454b-8a43-b24e62ea3be7@sirena.org.uk>
On 3/23/23 18:24, Mark Brown wrote:
> On Thu, Mar 23, 2023 at 09:55:47AM +0530, Anshuman Khandual wrote:
>> On 3/22/23 00:32, Mark Brown wrote:
>
>>> document a requirement for those traps to be disabled now in case we
>>> need them later, and do so during EL2 setup for KVM guests? That could
>>> always be done incrementally.
>
>> Unlike all other instruction trap enable fields in SYS_HFGITR_EL2, these BRBE
>> instructions ones are actually inverted in semantics i.e the particular fields
>> need to be set for these traps to be disabled in EL2.
>
> Right, for backwards compatibility all newly added fields are trap by
> default.
Okay
>
>> SYS_HFGITR_EL2.nBRBIALL
>> SYS_HFGITR_EL2.nBRBINJ
>
>> By default entire SYS_HFGITR_EL2 is set as cleared during init and that would
>> prevent a guest from using BRBE.
>
> It should prevent the host as well shouldn't it?
In a EL2 host environment, BRBE is being enabled either in EL2 (kernel/hv) or
in EL0 (user space), it never gets enabled on EL1. Moreover BRBIALL/BRBINJ
instructions are always executed while being inside EL2 (kernel/hv). Hence how
could these instructions cause trap in EL2 ?
>
>> I guess something like the following (untested) needs to be done, to enable
>> BRBE in guests.
>
>> + mrs x1, id_aa64dfr0_el1
>> + ubfx x1, x1, #ID_AA64DFR0_EL1_BRBE_SHIFT, #4
>> + cbz x1, .Lskip_brbe_\@
>> + mov x0, xzr
>> + orr x0, x0, #HFGITR_EL2_nBRBIALL
>> + orr x0, x0, #HFGITR_EL2_nBRBINJ
>> + msr_s SYS_HFGITR_EL2, x0
>> +
>> +.Lskip_brbe_\@:
>
> Yes, looks roughly what I'd expect.
I could send an stand alone patch after your latest series [1], which disables
BRBINJ/BRBIALL instruction trap in EL2 to enable BRBE usage in the guest.
https://lore.kernel.org/all/20230306-arm64-fgt-reg-gen-v3-2-decba93cbaab@kernel.org/T/
>
>>> I've got a patch adding the definition of that register to sysreg which
>>> I should be sending shortly, no need to duplicate that effort.
>
>> Sure, I assume you are moving the existing definition for SYS_HFGITR_EL2 along
>> with all its fields from ../include/asm/sysreg.h to ../tools/sysreg. Right, it
>> makes sense.
>
> No fields at the minute but yes, like the other conversions.
Sure.
next prev parent reply other threads:[~2023-03-24 3:20 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-15 5:14 [PATCH V9 00/10] arm64/perf: Enable branch stack sampling Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 01/10] drivers: perf: arm_pmu: Add new sched_task() callback Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 02/10] arm64/perf: Add BRBE registers and fields Anshuman Khandual
2023-04-12 8:32 ` Yang Shen
2023-05-15 6:22 ` Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 03/10] arm64/perf: Add branch stack support in struct arm_pmu Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 04/10] arm64/perf: Add branch stack support in struct pmu_hw_events Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 05/10] arm64/perf: Add branch stack support in ARMV8 PMU Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 06/10] arm64/perf: Enable branch stack events via FEAT_BRBE Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 07/10] arm64/perf: Add PERF_ATTACH_TASK_DATA to events with has_branch_stack() Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 08/10] arm64/perf: Add struct brbe_regset helper functions Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 09/10] arm64/perf: Implement branch records save on task sched out Anshuman Khandual
2023-03-15 5:14 ` [PATCH V9 10/10] arm64/perf: Implement branch records save on PMU IRQ Anshuman Khandual
2023-05-23 14:39 ` James Clark
2023-05-23 14:51 ` James Clark
2023-05-24 3:10 ` Anshuman Khandual
2023-03-21 19:02 ` [PATCH V9 00/10] arm64/perf: Enable branch stack sampling Mark Brown
2023-03-23 4:25 ` Anshuman Khandual
2023-03-23 12:54 ` Mark Brown
2023-03-24 3:20 ` Anshuman Khandual [this message]
2023-03-24 11:40 ` Mark Brown
2023-04-11 13:03 ` Will Deacon
2023-05-15 6:24 ` Anshuman Khandual
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