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From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] KVM/arm64: Don't emulate a PMU for 32-bit guests if feature not set
Date: Mon, 25 Apr 2022 18:14:13 +0100	[thread overview]
Message-ID: <875ymx9jbu.wl-maz@kernel.org> (raw)
In-Reply-To: <20220425145530.723858-1-alexandru.elisei@arm.com>

[+ Oliver]

Hi Alex,

On Mon, 25 Apr 2022 15:55:30 +0100,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> kvm->arch.arm_pmu is set when userspace attempts to set the first PMU
> attribute. As certain attributes are mandatory, arm_pmu ends up always
> being set to a valid arm_pmu, otherwise KVM will refuse to run the VCPU.
> However, this only happens if the VCPU has the PMU feature. If the VCPU
> doesn't have the feature bit set, kvm->arch.arm_pmu will be left
> uninitialized and equal to NULL.

Although I'm not opposed to this as an immediate workaround to avoid
the ugly crash, I think sanitising the AArch32 regs is the way to go.
Oliver had a stab at this a few weeks back[1], but this seem to have
stalled.

Could you have a look and see if anything was missing (the patches
needed some rework, but I haven't checked whether DFR0 was correctly
handled or not).

Thanks,

	M.

[1] https://lore.kernel.org/r/20220401010832.3425787-1-oupton@google.com

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
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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: james.morse@arm.com, suzuki.poulose@arm.com,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, Oliver Upton <oupton@google.com>
Subject: Re: [PATCH] KVM/arm64: Don't emulate a PMU for 32-bit guests if feature not set
Date: Mon, 25 Apr 2022 18:14:13 +0100	[thread overview]
Message-ID: <875ymx9jbu.wl-maz@kernel.org> (raw)
In-Reply-To: <20220425145530.723858-1-alexandru.elisei@arm.com>

[+ Oliver]

Hi Alex,

On Mon, 25 Apr 2022 15:55:30 +0100,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> kvm->arch.arm_pmu is set when userspace attempts to set the first PMU
> attribute. As certain attributes are mandatory, arm_pmu ends up always
> being set to a valid arm_pmu, otherwise KVM will refuse to run the VCPU.
> However, this only happens if the VCPU has the PMU feature. If the VCPU
> doesn't have the feature bit set, kvm->arch.arm_pmu will be left
> uninitialized and equal to NULL.

Although I'm not opposed to this as an immediate workaround to avoid
the ugly crash, I think sanitising the AArch32 regs is the way to go.
Oliver had a stab at this a few weeks back[1], but this seem to have
stalled.

Could you have a look and see if anything was missing (the patches
needed some rework, but I haven't checked whether DFR0 was correctly
handled or not).

Thanks,

	M.

[1] https://lore.kernel.org/r/20220401010832.3425787-1-oupton@google.com

-- 
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:[~2022-04-25 17:14 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-25 14:55 [PATCH] KVM/arm64: Don't emulate a PMU for 32-bit guests if feature not set Alexandru Elisei
2022-04-25 14:55 ` Alexandru Elisei
2022-04-25 17:14 ` Marc Zyngier [this message]
2022-04-25 17:14   ` Marc Zyngier
2022-04-25 17:26   ` Oliver Upton
2022-04-25 17:26     ` Oliver Upton
2022-04-26  9:30   ` Alexandru Elisei
2022-04-26  9:30     ` Alexandru Elisei
2022-04-26  8:05 ` Oliver Upton
2022-04-26  8:05   ` Oliver Upton
2022-04-26  9:01   ` Alexandru Elisei
2022-04-26  9:01     ` Alexandru Elisei
2022-04-27  7:57     ` Oliver Upton
2022-04-27  7:57       ` Oliver Upton
2022-04-27  9:45       ` Alexandru Elisei
2022-04-27  9:45         ` Alexandru Elisei
2022-04-27 21:10         ` Marc Zyngier
2022-04-27 21:10           ` Marc Zyngier
2022-04-28 19:58 ` Marc Zyngier
2022-04-28 19:58   ` Marc Zyngier

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