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From: James Morse <james.morse@arm.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: maz@kernel.org, linux-arm-kernel@lists.infradead.org,
	will@kernel.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature
Date: Thu, 19 Nov 2020 16:58:22 +0000	[thread overview]
Message-ID: <418e3bf6-159c-6d1f-2b84-2fdb10c3cddd@arm.com> (raw)
In-Reply-To: <20201027172705.15181-5-alexandru.elisei@arm.com>

Hi Alex,

On 27/10/2020 17:26, Alexandru Elisei wrote:
> Detect Statistical Profiling Extension (SPE) support using the cpufeatures
> framework. The presence of SPE is reported via the ARM64_SPE capability.
> 
> The feature will be necessary for emulating SPE in KVM, because KVM needs
> that all CPUs have SPE hardware to avoid scheduling a VCPU on a CPU without
> support. For this reason, the feature type ARM64_CPUCAP_SYSTEM_FEATURE has
> been selected to disallow hotplugging a CPU which doesn't support SPE.

Can you mention the existing driver in the commit message? Surprisingly it doesn't use
cpufeature at all. It looks like arm_spe_pmu_dev_init() goes out of its way to support
mismatched systems. (otherwise the significance of the new behaviour isn't clear!)

I read it as: the host is fine with mismatched systems, and the existing drivers supports
this. But KVM is not. After this patch you can't make the system mismatched 'late'.


Thanks,

James
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  reply	other threads:[~2020-11-19 16:58 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-27 17:26 [RFC PATCH v3 00/16] KVM: arm64: Add Statistical Profiling Extension (SPE) support Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 01/16] KVM: arm64: Initialize VCPU mdcr_el2 before loading it Alexandru Elisei
2020-11-19 16:58   ` James Morse
2020-12-02 14:25     ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 02/16] dt-bindings: ARM SPE: Highlight the need for PPI partitions on heterogeneous systems Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 03/16] KVM: arm64: Hide SPE from guests Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature Alexandru Elisei
2020-11-19 16:58   ` James Morse [this message]
2020-12-02 14:29     ` Alexandru Elisei
2020-12-02 17:23       ` Will Deacon
2020-12-03 10:07         ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 05/16] KVM: arm64: Introduce VCPU " Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 06/16] KVM: arm64: Introduce SPE primitives Alexandru Elisei
2020-11-19 16:58   ` James Morse
2020-12-02 15:13     ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 07/16] KVM: arm64: Define SPE data structure for each VCPU Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 08/16] KVM: arm64: Add a new VCPU device control group for SPE Alexandru Elisei
2020-11-05  9:58   ` Haibo Xu
2020-12-02 15:20     ` Alexandru Elisei
2020-11-19 16:58   ` James Morse
2020-12-02 16:28     ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 09/16] KVM: arm64: Use separate function for the mapping size in user_mem_abort() Alexandru Elisei
2020-11-05 10:01   ` Haibo Xu
2020-12-02 16:29     ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 10/16] KVM: arm64: Add a new VM device control group for SPE Alexandru Elisei
2020-11-05 10:10   ` Haibo Xu
2020-12-02 16:35     ` Alexandru Elisei
2020-11-19 16:59   ` James Morse
2021-03-23 14:27     ` Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 11/16] KVM: arm64: Add SPE system registers to VCPU context Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 12/16] KVM: arm64: VHE: Clear MDCR_EL2.E2PB in vcpu_put() Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 13/16] KVM: arm64: Switch SPE context on VM entry/exit Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 14/16] KVM: arm64: Emulate SPE buffer management interrupt Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 15/16] KVM: arm64: Enable SPE for guests Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 16/16] Documentation: arm64: Document ARM Neoverse-N1 erratum #1688567 Alexandru Elisei

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