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From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: mingo@redhat.com, tglx@linutronix.de, will@kernel.org,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute
Date: Wed, 08 Dec 2021 16:21:43 +0000	[thread overview]
Message-ID: <878rwv12zs.wl-maz@kernel.org> (raw)
In-Reply-To: <YbDZIfeOxYgRODGg@monolith.localdoman>

On Wed, 08 Dec 2021 16:11:13 +0000,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> > On the contrary, I am *very* happy to limit a VM to a single PMU (and
> > thus CPU) type on these systems. Really.
> 
> Ok, so any kind of asymmetry is unacceptable.
> 
> Accepted behaviour:
> 
> 1. If userspace sets PMU for one VCPU, then *all* other VCPUs must
> have a PMU set, and furthermore, it must be the same PMU as the
> first VCPU,
> 
> or
> 
> 2. If userspace has initialized a PMU (via
> KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_INIT)) without setting
> a PMU, then it is forbidden for userspace to set a PMU for the other
> VCPUs.
> 
> Is that what you had in mind?

Exactly. This sidesteps any sort of odd behaviour by forcing userspace
to pick a side.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Reiji Watanabe <reijiw@google.com>,
	james.morse@arm.com, suzuki.poulose@arm.com, will@kernel.org,
	mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, tglx@linutronix.de,
	mingo@redhat.com
Subject: Re: [PATCH v2 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute
Date: Wed, 08 Dec 2021 16:21:43 +0000	[thread overview]
Message-ID: <878rwv12zs.wl-maz@kernel.org> (raw)
In-Reply-To: <YbDZIfeOxYgRODGg@monolith.localdoman>

On Wed, 08 Dec 2021 16:11:13 +0000,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> > On the contrary, I am *very* happy to limit a VM to a single PMU (and
> > thus CPU) type on these systems. Really.
> 
> Ok, so any kind of asymmetry is unacceptable.
> 
> Accepted behaviour:
> 
> 1. If userspace sets PMU for one VCPU, then *all* other VCPUs must
> have a PMU set, and furthermore, it must be the same PMU as the
> first VCPU,
> 
> or
> 
> 2. If userspace has initialized a PMU (via
> KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_INIT)) without setting
> a PMU, then it is forbidden for userspace to set a PMU for the other
> VCPUs.
> 
> Is that what you had in mind?

Exactly. This sidesteps any sort of odd behaviour by forcing userspace
to pick a side.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-12-08 16:21 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-06 17:02 [PATCH v2 0/4] KVM: arm64: Improve PMU support on heterogeneous systems Alexandru Elisei
2021-12-06 17:02 ` Alexandru Elisei
2021-12-06 17:02 ` [PATCH v2 1/4] perf: Fix wrong name in comment for struct perf_cpu_context Alexandru Elisei
2021-12-06 17:02   ` Alexandru Elisei
2021-12-06 17:02 ` [PATCH v2 2/4] KVM: arm64: Keep a list of probed PMUs Alexandru Elisei
2021-12-06 17:02   ` Alexandru Elisei
2021-12-06 17:02 ` [PATCH v2 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute Alexandru Elisei
2021-12-06 17:02   ` Alexandru Elisei
2021-12-08  3:13   ` Reiji Watanabe
2021-12-08  3:13     ` Reiji Watanabe
2021-12-08 12:23     ` Alexandru Elisei
2021-12-08 12:23       ` Alexandru Elisei
2021-12-08 12:43       ` Alexandru Elisei
2021-12-08 12:43         ` Alexandru Elisei
2021-12-08 14:25       ` Marc Zyngier
2021-12-08 14:25         ` Marc Zyngier
2021-12-08 15:20         ` Alexandru Elisei
2021-12-08 15:20           ` Alexandru Elisei
2021-12-08 15:44           ` Marc Zyngier
2021-12-08 15:44             ` Marc Zyngier
2021-12-08 16:11             ` Alexandru Elisei
2021-12-08 16:11               ` Alexandru Elisei
2021-12-08 16:21               ` Marc Zyngier [this message]
2021-12-08 16:21                 ` Marc Zyngier
2021-12-06 17:02 ` [PATCH v2 4/4] KVM: arm64: Refuse to run VCPU if the PMU doesn't match the physical CPU Alexandru Elisei
2021-12-06 17:02   ` Alexandru Elisei
2021-12-07 14:17   ` Alexandru Elisei
2021-12-07 14:17     ` Alexandru Elisei
2021-12-08  7:54     ` Reiji Watanabe
2021-12-08  7:54       ` Reiji Watanabe
2021-12-08 10:38       ` Alexandru Elisei
2021-12-08 10:38         ` Alexandru Elisei
2021-12-13  7:40         ` Reiji Watanabe
2021-12-13  7:40           ` Reiji Watanabe
2021-12-08  9:56     ` Marc Zyngier
2021-12-08  9:56       ` Marc Zyngier
2021-12-08 11:18       ` Alexandru Elisei
2021-12-08 11:18         ` Alexandru Elisei
2021-12-08  2:36 ` [PATCH v2 0/4] KVM: arm64: Improve PMU support on heterogeneous systems Reiji Watanabe
2021-12-08  2:36   ` Reiji Watanabe
2021-12-08  8:05   ` Marc Zyngier
2021-12-08  8:05     ` Marc Zyngier
2021-12-13  6:36     ` Reiji Watanabe
2021-12-13  6:36       ` Reiji Watanabe
2021-12-13 11:14       ` Alexandru Elisei
2021-12-13 11:14         ` Alexandru Elisei
2021-12-14  6:24         ` Reiji Watanabe
2021-12-14  6:24           ` Reiji Watanabe
2021-12-14 11:56           ` Marc Zyngier
2021-12-14 11:56             ` Marc Zyngier
2021-12-15  6:47             ` Reiji Watanabe
2021-12-15  6:47               ` Reiji Watanabe

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