From: Will Deacon <will@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: maz@kernel.org, linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature
Date: Wed, 2 Dec 2020 17:23:53 +0000 [thread overview]
Message-ID: <20201202172353.GB29813@willie-the-truck> (raw)
In-Reply-To: <906a02c2-3923-3542-ffb8-43d856498e07@arm.com>
On Wed, Dec 02, 2020 at 02:29:31PM +0000, Alexandru Elisei wrote:
> On 11/19/20 4:58 PM, James Morse wrote:
> > 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'.
>
> That was exactly my intention. Certainly, I'll try to make the commit message
> clearer by mentioning the SPE driver.
Hmm, so are you saying that with this patch applied, a machine where KVM
isn't even being used can no longer late-online CPUs without SPE if the boot
CPUs had it? If so, then I don't think that's acceptable, unfortunately.
As James points out, the current driver is very careful to support
big.LITTLE misconfigurations and I don't see why KVM support should change
that.
Will
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WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: suzuki.poulose@arm.com, maz@kernel.org,
James Morse <james.morse@arm.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, julien.thierry.kdev@gmail.com
Subject: Re: [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature
Date: Wed, 2 Dec 2020 17:23:53 +0000 [thread overview]
Message-ID: <20201202172353.GB29813@willie-the-truck> (raw)
In-Reply-To: <906a02c2-3923-3542-ffb8-43d856498e07@arm.com>
On Wed, Dec 02, 2020 at 02:29:31PM +0000, Alexandru Elisei wrote:
> On 11/19/20 4:58 PM, James Morse wrote:
> > 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'.
>
> That was exactly my intention. Certainly, I'll try to make the commit message
> clearer by mentioning the SPE driver.
Hmm, so are you saying that with this patch applied, a machine where KVM
isn't even being used can no longer late-online CPUs without SPE if the boot
CPUs had it? If so, then I don't think that's acceptable, unfortunately.
As James points out, the current driver is very careful to support
big.LITTLE misconfigurations and I don't see why KVM support should change
that.
Will
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-12-02 17:24 UTC|newest]
Thread overview: 70+ 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 ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 01/16] KVM: arm64: Initialize VCPU mdcr_el2 before loading it Alexandru Elisei
2020-10-27 17:26 ` Alexandru Elisei
2020-11-19 16:58 ` James Morse
2020-11-19 16:58 ` James Morse
2020-12-02 14:25 ` Alexandru Elisei
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 ` 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 ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature Alexandru Elisei
2020-10-27 17:26 ` Alexandru Elisei
2020-11-19 16:58 ` James Morse
2020-11-19 16:58 ` James Morse
2020-12-02 14:29 ` Alexandru Elisei
2020-12-02 14:29 ` Alexandru Elisei
2020-12-02 17:23 ` Will Deacon [this message]
2020-12-02 17:23 ` Will Deacon
2020-12-03 10:07 ` Alexandru Elisei
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 ` Alexandru Elisei
2020-10-27 17:26 ` [RFC PATCH v3 06/16] KVM: arm64: Introduce SPE primitives Alexandru Elisei
2020-10-27 17:26 ` Alexandru Elisei
2020-11-19 16:58 ` James Morse
2020-11-19 16:58 ` James Morse
2020-12-02 15:13 ` Alexandru Elisei
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 ` 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
2020-10-27 17:26 ` Alexandru Elisei
2020-11-05 9:58 ` Haibo Xu
2020-11-05 9:58 ` Haibo Xu
2020-12-02 15:20 ` Alexandru Elisei
2020-12-02 15:20 ` Alexandru Elisei
2020-11-19 16:58 ` James Morse
2020-11-19 16:58 ` James Morse
2020-12-02 16:28 ` Alexandru Elisei
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
2020-10-27 17:26 ` Alexandru Elisei
2020-11-05 10:01 ` Haibo Xu
2020-11-05 10:01 ` Haibo Xu
2020-12-02 16:29 ` Alexandru Elisei
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
2020-10-27 17:26 ` Alexandru Elisei
2020-11-05 10:10 ` Haibo Xu
2020-11-05 10:10 ` Haibo Xu
2020-12-02 16:35 ` Alexandru Elisei
2020-12-02 16:35 ` Alexandru Elisei
2020-11-19 16:59 ` James Morse
2020-11-19 16:59 ` James Morse
2021-03-23 14:27 ` Alexandru Elisei
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 ` 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 ` 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 ` 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 ` 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 ` Alexandru Elisei
2020-10-27 17:27 ` [RFC PATCH v3 16/16] Documentation: arm64: Document ARM Neoverse-N1 erratum #1688567 Alexandru Elisei
2020-10-27 17:27 ` Alexandru Elisei
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