linux-kernel - Re: [PATCH v3 02/14] arm64: Detect if in a realm and set RIPAS RAM

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Date: Wed, 12 Jun 2024 11:40:23 +0100
From: Jean-Philippe Brucker <jean-philippe@...aro.org>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v3 02/14] arm64: Detect if in a realm and set RIPAS RAM

On Wed, Jun 05, 2024 at 10:29:54AM +0100, Steven Price wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> Detect that the VM is a realm guest by the presence of the RSI
> interface.
> 
> If in a realm then all memory needs to be marked as RIPAS RAM initially,
> the loader may or may not have done this for us. To be sure iterate over
> all RAM and mark it as such. Any failure is fatal as that implies the
> RAM regions passed to Linux are incorrect - which would mean failing
> later when attempting to access non-existent RAM.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Co-developed-by: Steven Price <steven.price@....com>
> Signed-off-by: Steven Price <steven.price@....com>

> +static bool rsi_version_matches(void)
> +{
> +	unsigned long ver_lower, ver_higher;
> +	unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
> +						&ver_lower,
> +						&ver_higher);

There is a regression on QEMU TCG (in emulation mode, not running under KVM):

  qemu-system-aarch64 -M virt -cpu max -kernel Image -nographic

This doesn't implement EL3 or EL2, so SMC is UNDEFINED (DDI0487J.a R_HMXQS),
and we end up with an undef instruction exception. So this patch would
also break hardware that only implements EL1 (I don't know if it exists).

The easiest fix is to detect the SMC conduit through the PSCI node in DT.
SMCCC helpers already do this, but we can't use them this early in the
boot. I tested adding an early probe to the PSCI driver to check this, see
attached patches.

Note that we do need to test the conduit after finding a PSCI node,
because even though it doesn't implement EL2 in this configuration, QEMU
still accepts PSCI HVCs in order to support SMP.

Thanks,
Jean


View attachment "0001-firmware-psci-Add-psci_early_test_conduit.patch" of type "text/plain" (2590 bytes)

View attachment "0002-squash-arm64-Detect-if-in-a-realm-and-set-RIPAS-RAM.patch" of type "text/plain" (1702 bytes)