From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH 05/12] arm64: cpufeature: Detect E2H0 not being implemented
Date: Fri, 17 Nov 2023 12:21:30 +0000 [thread overview]
Message-ID: <86v8a0zi2d.wl-maz@kernel.org> (raw)
In-Reply-To: <ZVa6RIOT8Eixqy6l@thinky-boi>
On Fri, 17 Nov 2023 00:56:36 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
>
> On Mon, Nov 13, 2023 at 05:42:37PM +0000, Marc Zyngier wrote:
> > FEAT_E2H0 is a new feature that indicates whether or not HCR_EL2.E2H
> > can be set to 0. Amusingly, this feature is set to 0 when implemented,
> > and otherwise negative.
> >
> > Add a new capability and detection infrastructure to detect the
> > absence of FEAT_E2H0.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
>
> > ---
> > arch/arm64/kernel/cpufeature.c | 7 +++++++
> > arch/arm64/tools/cpucaps | 1 +
> > 2 files changed, 8 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 41db7f993eef..e0d64e8b4851 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -2787,6 +2787,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> > .matches = has_cpuid_feature,
> > ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, EVT, IMP)
> > },
> > + {
> > + .desc = "FEAT_E2H0 not implemented",
> > + .capability = ARM64_HCR_E2H_RES1,
>
> I did read this a couple times before the neurons that interpret "0 not
> implemented" and "RES1" fired together, heh.
Yeah, the whole thing is upside down, in order to preserve backward
compatibility. I guess that as the architecture deprecates old cruft,
we may see more of this sort of constructs.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2023-11-17 12:22 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-13 17:42 [PATCH 00/12] arm64: Add support for FEAT_E2H0, or lack thereof Marc Zyngier
2023-11-13 17:42 ` [PATCH 01/12] arm64: cpufeatures: Correctly handle signed values Marc Zyngier
2023-11-17 0:45 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 02/12] arm64: cpufeature: Correctly display signed override values Marc Zyngier
2023-11-17 0:46 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 03/12] arm64: sysreg: Add layout for ID_AA64MMFR4_EL1 Marc Zyngier
2023-11-13 17:42 ` [PATCH 04/12] arm64: cpufeature: Add ID_AA64MMFR4_EL1 handling Marc Zyngier
2023-11-17 0:48 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 05/12] arm64: cpufeature: Detect E2H0 not being implemented Marc Zyngier
2023-11-17 0:56 ` Oliver Upton
2023-11-17 12:21 ` Marc Zyngier [this message]
2023-11-13 17:42 ` [PATCH 06/12] arm64: cpufeature: Detect HCR_EL2.NV1 being RES0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 07/12] arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is non-zero Marc Zyngier
2023-11-17 0:23 ` Oliver Upton
2023-11-17 12:17 ` Marc Zyngier
2023-11-17 18:01 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 08/12] arm64: Add override for ID_AA64MMFR4_EL1.E2H0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 09/12] arm64: Add MIDR-based override infrastructure Marc Zyngier
2023-11-13 17:42 ` [PATCH 10/12] arm64: Add MIDR-based overrides for ID_AA64MMFR4_EL1.E2H0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 11/12] KVM: arm64: Expose ID_AA64MMFR4_EL1 to guests Marc Zyngier
2023-11-13 17:42 ` [PATCH 12/12] KVM: arm64: Force guest's HCR_EL2.E2H RES1 when NV1 is not implemented Marc Zyngier
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