Re: [PATCH] arm64: Fix early handling of FEAT_E2H0 not being implemented

From: Catalin Marinas <catalin.marinas@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH] arm64: Fix early handling of FEAT_E2H0 not being implemented
Date: Thu, 21 Mar 2024 20:16:15 +0000	[thread overview]
Message-ID: <ZfyVj8txU6WngPGH@arm.com> (raw)
In-Reply-To: <20240321115414.3169115-1-maz@kernel.org>

On Thu, Mar 21, 2024 at 11:54:14AM +0000, Marc Zyngier wrote:
> Commit 3944382fa6f2 introduced checks for the FEAT_E2H0 not being
> implemented. However, the check is absolutely wrong and makes a
> point it testing a bit that is guaranteed to be zero.
> 
> On top of that, the detection happens way too late, after the
> init_el2_state has done its job.
> 
> This went undetected because the HW this was tested on has E2H being
> RAO/WI, and not RES1. However, the bug shows up when run as a nested
> guest, where HCR_EL2.E2H is not necessarily set to 1. As a result,
> booting the kernel in hVHE mode fails with timer accesses being
> cought in a trap loop (which was fun to debug).
> 
> Fix the check for ID_AA64MMFR4_EL1.E2H0, and set the HCR_EL2.E2H bit
> early so that it can be checked by the rest of the init sequence.
> 
> With this, hVHE works again in a NV environment that doesn't have
> FEAT_E2H0.
> 
> Fixes: 3944382fa6f2 ("arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is negative")
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

I assume Oliver will take it, otherwise I can pick it up after -rc1
since I don't have the fixed commit in my tree.

-- 
Catalin