From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Eric Auger <eric.auger@redhat.com>,
kernel-team@android.com
Subject: Re: [PATCH v2 6/7] KVM: arm64: Upgrade PMU support to ARMv8.4
Date: Wed, 27 Jan 2021 14:35:23 +0000 [thread overview]
Message-ID: <1b594e7b1f47e372ea84f759507db0b9@kernel.org> (raw)
In-Reply-To: <59700102-5340-b5ec-28e2-d95ee3e59c6b@arm.com>
Hi Alex,
On 2021-01-27 14:09, Alexandru Elisei wrote:
> Hi Marc,
>
> On 1/25/21 12:26 PM, Marc Zyngier wrote:
>> Upgrading the PMU code from ARMv8.1 to ARMv8.4 turns out to be
>> pretty easy. All that is required is support for PMMIR_EL1, which
>> is read-only, and for which returning 0 is a valid option as long
>> as we don't advertise STALL_SLOT as an implemented event.
>
> According to ARM DDI 0487F.b, page D7-2743:
>
> "If ARMv8.4-PMU is implemented:
> - If STALL_SLOT is not implemented, it is IMPLEMENTATION DEFINED
> whether the PMMIR
> System registers are implemented.
> - If STALL_SLOT is implemented, then the PMMIR System registers are
> implemented."
>
> I tried to come up with a reason why PMMIR is emulated instead of being
> left
> undefined, but I couldn't figure it out. Would you mind adding a
> comment or
> changing the commit message to explain that?
The main reason is that PMMIR gets new fields down the line,
and doing the bare minimum in term of implementation allows
us to gently ease into it.
We could also go for the full PMMIR reporting on homogeneous
systems too, as a further improvement.
What do you think?
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2021-01-27 14:38 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 12:26 [PATCH v2 0/7] KVM: arm64: More PMU/debug ID register fixes Marc Zyngier
2021-01-25 12:26 ` [PATCH v2 1/7] KVM: arm64: Fix missing RES1 in emulation of DBGBIDR Marc Zyngier
2021-01-26 17:32 ` Alexandru Elisei
2021-01-25 12:26 ` [PATCH v2 2/7] KVM: arm64: Fix AArch32 PMUv3 capping Marc Zyngier
2021-01-26 17:35 ` Alexandru Elisei
2021-01-25 12:26 ` [PATCH v2 3/7] KVM: arm64: Add handling of AArch32 PCMEID{2,3} PMUv3 registers Marc Zyngier
2021-01-25 12:26 ` [PATCH v2 4/7] KVM: arm64: Refactor filtering of ID registers Marc Zyngier
2021-01-27 12:12 ` Alexandru Elisei
2021-01-25 12:26 ` [PATCH v2 5/7] KVM: arm64: Limit the debug architecture to ARMv8.0 Marc Zyngier
2021-01-27 12:18 ` Alexandru Elisei
2021-01-25 12:26 ` [PATCH v2 6/7] KVM: arm64: Upgrade PMU support to ARMv8.4 Marc Zyngier
2021-01-27 14:09 ` Alexandru Elisei
2021-01-27 14:35 ` Marc Zyngier [this message]
2021-01-27 17:00 ` Alexandru Elisei
2021-01-27 17:23 ` Marc Zyngier
2021-01-27 17:41 ` Alexandru Elisei
2021-02-03 10:32 ` Marc Zyngier
2021-02-03 17:29 ` Alexandru Elisei
2021-01-27 17:53 ` Auger Eric
2021-02-03 10:36 ` Marc Zyngier
2021-02-03 11:07 ` Auger Eric
2021-02-03 11:20 ` Marc Zyngier
2021-02-03 12:39 ` Auger Eric
2021-02-03 13:28 ` Marc Zyngier
2021-02-04 12:32 ` Alexandru Elisei
2021-02-04 14:21 ` Marc Zyngier
2021-01-25 12:26 ` [PATCH v2 7/7] KVM: arm64: Use symbolic names for the PMU versions Marc Zyngier
2021-01-27 14:28 ` Alexandru Elisei
2021-01-27 17:56 ` Auger Eric
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