From: Marc Zyngier <maz@kernel.org>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: kvm@vger.kernel.org, kernel-team@android.com,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
Date: Fri, 01 Oct 2021 15:54:08 +0100 [thread overview]
Message-ID: <87ee94ssmn.wl-maz@kernel.org> (raw)
In-Reply-To: <e80b2454-45c3-19a3-7a96-dcb484f9e2f5@arm.com>
On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >>
> >>> + if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >>
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> >
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
>
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
>
> That said, I am happy to leave this as is and the doc says so.
I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).
I'll respin the patch with this change.
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: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu, ascull@google.com,
dbrazdil@google.com, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kernel-team@android.com
Subject: Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
Date: Fri, 01 Oct 2021 15:54:08 +0100 [thread overview]
Message-ID: <87ee94ssmn.wl-maz@kernel.org> (raw)
In-Reply-To: <e80b2454-45c3-19a3-7a96-dcb484f9e2f5@arm.com>
On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >>
> >>> + if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >>
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> >
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
>
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
>
> That said, I am happy to leave this as is and the doc says so.
I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).
I'll respin the patch with this change.
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
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu, ascull@google.com,
dbrazdil@google.com, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kernel-team@android.com
Subject: Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
Date: Fri, 01 Oct 2021 15:54:08 +0100 [thread overview]
Message-ID: <87ee94ssmn.wl-maz@kernel.org> (raw)
In-Reply-To: <e80b2454-45c3-19a3-7a96-dcb484f9e2f5@arm.com>
On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >>
> >>> + if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >>
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> >
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
>
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
>
> That said, I am happy to leave this as is and the doc says so.
I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).
I'll respin the patch with this change.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2021-10-01 14:54 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 9:16 [PATCH] KVM: arm64: Allow KVM to be disabled from the command line Marc Zyngier
2021-09-03 9:16 ` Marc Zyngier
2021-09-03 9:16 ` Marc Zyngier
2021-09-28 14:58 ` David Brazdil
2021-09-28 14:58 ` David Brazdil
2021-09-28 14:58 ` David Brazdil
2021-09-30 10:22 ` Marc Zyngier
2021-09-30 10:22 ` Marc Zyngier
2021-09-30 10:22 ` Marc Zyngier
2021-09-29 10:28 ` Will Deacon
2021-09-29 10:28 ` Will Deacon
2021-09-29 10:28 ` Will Deacon
2021-09-29 10:35 ` Suzuki K Poulose
2021-09-29 10:35 ` Suzuki K Poulose
2021-09-29 10:35 ` Suzuki K Poulose
2021-09-30 10:29 ` Marc Zyngier
2021-09-30 10:29 ` Marc Zyngier
2021-09-30 10:29 ` Marc Zyngier
2021-10-01 9:27 ` Suzuki K Poulose
2021-10-01 9:27 ` Suzuki K Poulose
2021-10-01 9:27 ` Suzuki K Poulose
2021-10-01 14:54 ` Marc Zyngier [this message]
2021-10-01 14:54 ` Marc Zyngier
2021-10-01 14:54 ` Marc Zyngier
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