6.15-stable review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 78b23877dbba7dbcda2b89383d17bed82ce8f663 ]
The fp-ptrace test suite expects that FPMR is set to zero when PSTATE.SM is changed via ptrace, but ptrace has never altered FPMR in this way, and the test logic erroneously relies upon (and has concealed) a bug where task_fpsimd_load() would unexpectedly and non-deterministically clobber FPMR.
Using ptrace, FPMR can only be altered by writing to the NT_ARM_FPMR regset. The value of PSTATE.SM can be altered by writing to the NT_ARM_SVE or NT_ARM_SSVE regsets, and/or by changing the SME vector length (when writing to the NT_ARM_SVE, NT_ARM_SSVE, or NT_ARM_ZA regsets), but none of these writes will change the value of FPMR.
The task_fpsimd_load() bug was introduced with the initial FPMR support in commit:
203f2b95a882 ("arm64/fpsimd: Support FEAT_FPMR")
The incorrect FPMR test code was introduced in commit:
7dbd26d0b22d ("kselftest/arm64: Add FPMR coverage to fp-ptrace")
Subsequently, the task_fpsimd_load() bug was fixed in commit:
e5fa85fce08b ("arm64/fpsimd: Don't corrupt FPMR when streaming mode changes")
... whereupon the fp-ptrace FPMR tests started failing reliably, e.g.
| # # Mismatch in saved FPMR: 915058000 != 0 | # not ok 25 SVE write, SVE 64->64, SME 64/0->64/1
Fix this by changing the test to expect that FPMR is *NOT* changed when PSTATE.SM is changed via ptrace, matching the extant behaviour.
I've chosen to update the test code rather than modifying ptrace to zero FPMR when PSTATE.SM changes. Not zeroing FPMR is simpler overall, and allows the NT_ARM_FPMR regset to be handled independently from other regsets, leaving less scope for error.
Fixes: 7dbd26d0b22d ("kselftest/arm64: Add FPMR coverage to fp-ptrace") Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: David Spickett david.spickett@arm.com Cc: Luis Machado luis.machado@arm.com Cc: Marc Zyngier maz@kernel.org Cc: Mark Brown broonie@kernel.org Cc: Will Deacon will@kernel.org Link: https://lore.kernel.org/r/20250508132644.1395904-22-mark.rutland@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/arm64/fp/fp-ptrace.c | 14 +------------- 1 file changed, 1 insertion(+), 13 deletions(-)
diff --git a/tools/testing/selftests/arm64/fp/fp-ptrace.c b/tools/testing/selftests/arm64/fp/fp-ptrace.c index 4930e03a7b990..762048eb354ff 100644 --- a/tools/testing/selftests/arm64/fp/fp-ptrace.c +++ b/tools/testing/selftests/arm64/fp/fp-ptrace.c @@ -891,18 +891,11 @@ static void set_initial_values(struct test_config *config) { int vq = __sve_vq_from_vl(vl_in(config)); int sme_vq = __sve_vq_from_vl(config->sme_vl_in); - bool sm_change;
svcr_in = config->svcr_in; svcr_expected = config->svcr_expected; svcr_out = 0;
- if (sme_supported() && - (svcr_in & SVCR_SM) != (svcr_expected & SVCR_SM)) - sm_change = true; - else - sm_change = false; - fill_random(&v_in, sizeof(v_in)); memcpy(v_expected, v_in, sizeof(v_in)); memset(v_out, 0, sizeof(v_out)); @@ -953,12 +946,7 @@ static void set_initial_values(struct test_config *config) if (fpmr_supported()) { fill_random(&fpmr_in, sizeof(fpmr_in)); fpmr_in &= FPMR_SAFE_BITS; - - /* Entering or exiting streaming mode clears FPMR */ - if (sm_change) - fpmr_expected = 0; - else - fpmr_expected = fpmr_in; + fpmr_expected = fpmr_in; } else { fpmr_in = 0; fpmr_expected = 0;