Re: [PATCH v21 15/15] KVM: selftests: arm64: Add GCS EXLOCK exception emulation test

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kselftest/arm64: missing fine-grained trap tests mentioned in commit message
--

commit c63cb70f3a95d5f56914bee1163a8ae38fd9251f
Author: Mark Brown <broonie@kernel.org>

KVM: selftests: arm64: Add GCS EXLOCK exception emulation test

This commit adds a new selftest to validate the emulation of
GCSCR_EL2.EXLOCKEN behavior during exception return (ERET) for KVM on arm64.
It checks that expected exceptions are generated and verifies system register
interactions.

> We nest handling of two UDFs to allow us to both observe and modify
> PSTATE.EXLOCK, checking that expected exceptions are generated for ERET.
> We also repeat the UDF tests having enabled fine grained traps for ERET
> to try to ensure that the slow paths are taken.

[ ... ]

> diff --git a/tools/testing/selftests/kvm/arm64/gcs_exceptions.c b/tools/testing/selftests/kvm/arm64/gcs_exceptions.c
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/arm64/gcs_exceptions.c

[ ... ]

> +static void guest_code(void)
> +{
> +	GUEST_ASSERT_EQ(get_current_el(), 2);
> +
> +	/*
> +	 * Try straightforwardly generating an exception without and
> +	 * with EXLOCK.
> +	 */
> +	test_udf_exception(false);
> +	test_sysreg(UDF_ELR_EL1, false);
> +	test_sysreg(UDF_ELR_EL2, false);
> +	test_sysreg(UDF_SPSR_EL1, false);
> +	test_sysreg(UDF_SPSR_EL2, false);
> +
> +	test_udf_exception(true);
> +	test_sysreg(UDF_ELR_EL1, true);
> +	test_sysreg(UDF_ELR_EL2, true);
> +	test_sysreg(UDF_SPSR_EL1, true);
> +	test_sysreg(UDF_SPSR_EL2, true);
> +
> +	GUEST_DONE();
> +}

[Severity: Medium]
Is the fine-grained trap testing missing here? The commit message explicitly
states that the UDF tests are repeated with fine-grained traps enabled for
ERET to ensure slow paths are taken.

However, looking at the guest_code() implementation in
tools/testing/selftests/kvm/arm64/gcs_exceptions.c, the tests are only
executed with the enable_exlock parameter set to false and then true. There
does not appear to be any logic to configure fine-grained trap registers
(such as HFGITR_EL2) or an additional pass to repeat these UDF tests with
those traps active.

Does the test need an update to match the commit message, or is this
handled in a different way?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260930-arm64-gcs-v21-0-3556644cd927@kernel.org?part=15