Re: [PATCH v4 00/10] arm64: Add support for FEAT_E2H0, or lack thereof

From: Catalin Marinas <catalin.marinas@arm.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	James Morse <james.morse@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH v4 00/10] arm64: Add support for FEAT_E2H0, or lack thereof
Date: Thu, 8 Feb 2024 12:30:20 +0000	[thread overview]
Message-ID: <ZcTJXBThmtRmNbG8@arm.com> (raw)
In-Reply-To: <Zb08fXz23JUiF4hD@linux.dev>

On Fri, Feb 02, 2024 at 07:03:25PM +0000, Oliver Upton wrote:
> On Mon, Jan 22, 2024 at 06:13:34PM +0000, Marc Zyngier wrote:
> > Since ARMv8.1, the architecture has grown the VHE feature, which makes
> > EL2 a superset of EL1. With ARMv9.5 (and retroactively allowed from
> > ARMv8.1), the architecture allows implementations to have VHE as the
> > *only* implemented behaviour, meaning that HCR_EL2.E2H can be
> > implemented as RES1. As a follow-up, HCR_EL2.NV1 can also be
> > implemented as RES0, making the VHE-ness of the architecture
> > recursive.
> > 
> > This has a number of consequences, both at boot time and for KVM,
> > though the changes at that level are pretty minor.
> > 
> > The real meat of this series is on the cpufeature front, as FEAT_E2H0
> > is a *negative* feature, where 0b1111 (-1) represents E2H being RES1
> > and 0b1110 (-2) additionally indicates that NV1 is RES0. Fun, isn't
> > it?
> 
> This looks good to me. Catalin + Will, are you comfortable with the
> cpufeature changes at this point?

Yes, I acked those touching the arm64 files.

> No strong opinions on which tree these patches get applied to. Most of
> the series is non-KVM code, so I'd understand if y'all wanted it to go
> through arm64. OTOH, there are some other KVM features that might appear
> in 6.9 that build on top of this, so at minimum I'd probably need a
> shared branch.

Please take it through the arm64 kvm tree but keep it on a separate
stable branch in case I need to pull it.

-- 
Catalin

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