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From: Marc Zyngier <maz@kernel.org>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: David Brazdil <dbrazdil@google.com>,
	kvmarm@lists.cs.columbia.edu, Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	kernel-team@android.com, Will Deacon <will@kernel.org>,
	Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return
Date: Wed, 30 Dec 2020 10:06:19 +0000	[thread overview]
Message-ID: <0e1d555404e4ae8edcf6737735dc0eb7@kernel.org> (raw)
In-Reply-To: <20201229170412.GN1551@shell.armlinux.org.uk>

On 2020-12-29 17:04, Russell King - ARM Linux admin wrote:
> On Tue, Dec 29, 2020 at 04:00:59PM +0000, David Brazdil wrote:
>> The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET 
>> should
>> not return, as dictated by the PSCI spec. However, there is firmware 
>> out
>> there which breaks this assumption, leading to a hyp panic. Make KVM
>> more robust to broken firmware by allowing these to return.
> 
> Are you sure you should just return?
> 
> We've had issues in the past with Linux reboot(2) that returns
> to userspace, allowing on 32-bit ARM for example watchdogs to
> unexpectedly continue being serviced.

I don't think this changes anything compared to the case where
the PSCI relay isn't enabled. The EL1 part of the kernel would
see the SYSTEM_RESET call return, and handle it accordingly
(stay in a while(1) loop).

This is consistent with the PSCI relay design goal of being
invisible to the EL1 kernel.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, Sudeep Holla <sudeep.holla@arm.com>,
	kernel-team@android.com, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return
Date: Wed, 30 Dec 2020 10:06:19 +0000	[thread overview]
Message-ID: <0e1d555404e4ae8edcf6737735dc0eb7@kernel.org> (raw)
In-Reply-To: <20201229170412.GN1551@shell.armlinux.org.uk>

On 2020-12-29 17:04, Russell King - ARM Linux admin wrote:
> On Tue, Dec 29, 2020 at 04:00:59PM +0000, David Brazdil wrote:
>> The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET 
>> should
>> not return, as dictated by the PSCI spec. However, there is firmware 
>> out
>> there which breaks this assumption, leading to a hyp panic. Make KVM
>> more robust to broken firmware by allowing these to return.
> 
> Are you sure you should just return?
> 
> We've had issues in the past with Linux reboot(2) that returns
> to userspace, allowing on 32-bit ARM for example watchdogs to
> unexpectedly continue being serviced.

I don't think this changes anything compared to the case where
the PSCI relay isn't enabled. The EL1 part of the kernel would
see the SYSTEM_RESET call return, and handle it accordingly
(stay in a while(1) loop).

This is consistent with the PSCI relay design goal of being
invisible to the EL1 kernel.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
_______________________________________________
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: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Will Deacon <will@kernel.org>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	David Brazdil <dbrazdil@google.com>,
	kernel-team@android.com, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return
Date: Wed, 30 Dec 2020 10:06:19 +0000	[thread overview]
Message-ID: <0e1d555404e4ae8edcf6737735dc0eb7@kernel.org> (raw)
In-Reply-To: <20201229170412.GN1551@shell.armlinux.org.uk>

On 2020-12-29 17:04, Russell King - ARM Linux admin wrote:
> On Tue, Dec 29, 2020 at 04:00:59PM +0000, David Brazdil wrote:
>> The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET 
>> should
>> not return, as dictated by the PSCI spec. However, there is firmware 
>> out
>> there which breaks this assumption, leading to a hyp panic. Make KVM
>> more robust to broken firmware by allowing these to return.
> 
> Are you sure you should just return?
> 
> We've had issues in the past with Linux reboot(2) that returns
> to userspace, allowing on 32-bit ARM for example watchdogs to
> unexpectedly continue being serviced.

I don't think this changes anything compared to the case where
the PSCI relay isn't enabled. The EL1 part of the kernel would
see the SYSTEM_RESET call return, and handle it accordingly
(stay in a while(1) loop).

This is consistent with the PSCI relay design goal of being
invisible to the EL1 kernel.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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

  reply	other threads:[~2020-12-30 10:08 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-29 16:00 [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return David Brazdil
2020-12-29 16:00 ` David Brazdil
2020-12-29 16:00 ` David Brazdil
2020-12-29 17:04 ` Russell King - ARM Linux admin
2020-12-29 17:04   ` Russell King - ARM Linux admin
2020-12-29 17:04   ` Russell King - ARM Linux admin
2020-12-30 10:06   ` Marc Zyngier [this message]
2020-12-30 10:06     ` Marc Zyngier
2020-12-30 10:06     ` Marc Zyngier
2020-12-29 17:16 ` Marc Zyngier
2020-12-29 17:16   ` Marc Zyngier
2020-12-29 17:16   ` Marc Zyngier
2020-12-30 11:03   ` David Brazdil
2020-12-30 11:03     ` David Brazdil
2020-12-30 11:03     ` David Brazdil
2021-01-15 11:33 ` Marc Zyngier
2021-01-15 11:33   ` Marc Zyngier
2021-01-15 11:33   ` Marc Zyngier

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