linux-kernel - [PATCH 4/5] kselftst/arm64: Test NT_ARM_SVE FPSIMD format writes on non-SVE systems

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Message-Id: <20250820-arm64-sme-ptrace-sme-only-v1-4-f7c22b2871f8@kernel.org>
Date: Wed, 20 Aug 2025 19:29:06 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Shuah Khan <shuah@...nel.org>, 
 Jonathan Corbet <corbet@....net>, Oleg Nesterov <oleg@...hat.com>
Cc: Mark Rutland <mark.rutland@....com>, 
 David Spickett <david.spickett@....com>, 
 Thiago Jung Bauermann <thiago.bauermann@...aro.org>, 
 Luis Machado <luis.machado.foss@...il.com>, 
 linux-arm-kernel@...ts.infradead.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH 4/5] kselftst/arm64: Test NT_ARM_SVE FPSIMD format writes
 on non-SVE systems

In order to allow exiting streaming mode on systems with SME but not SVE
we allow writes of FPSIMD format data via NT_ARM_SVE even when SVE is not
supported, add a test case that covers this to sve-ptrace.

We do not support reads.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
 tools/testing/selftests/arm64/fp/sve-ptrace.c | 61 +++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/tools/testing/selftests/arm64/fp/sve-ptrace.c b/tools/testing/selftests/arm64/fp/sve-ptrace.c
index 5f39ca0b4194..fe43fb07ee6c 100644
--- a/tools/testing/selftests/arm64/fp/sve-ptrace.c
+++ b/tools/testing/selftests/arm64/fp/sve-ptrace.c
@@ -378,6 +378,58 @@ static void ptrace_sve_fpsimd(pid_t child, const struct vec_type *type)
 	free(svebuf);
 }
 
+/* Write the FPSIMD registers via the SVE regset when SVE is not supported */
+static void ptrace_sve_fpsimd_no_sve(pid_t child)
+{
+	void *svebuf;
+	struct user_sve_header *sve;
+	struct user_fpsimd_state *fpsimd, new_fpsimd;
+	unsigned int i, j;
+	unsigned char *p;
+	int ret;
+
+	svebuf = malloc(SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD));
+	if (!svebuf) {
+		ksft_test_result_fail("Failed to allocate FPSIMD buffer\n");
+		return;
+	}
+
+	/* On a system without SVE the VL should be set to 0 */
+	memset(svebuf, 0, SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD));
+	sve = svebuf;
+	sve->flags = SVE_PT_REGS_FPSIMD;
+	sve->size = SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD);
+	sve->vl = 0;
+
+	/* Try to set a known FPSIMD state via PT_REGS_SVE */
+	fpsimd = (struct user_fpsimd_state *)((char *)sve +
+					      SVE_PT_FPSIMD_OFFSET);
+	for (i = 0; i < 32; ++i) {
+		p = (unsigned char *)&fpsimd->vregs[i];
+
+		for (j = 0; j < sizeof(fpsimd->vregs[i]); ++j)
+			p[j] = j;
+	}
+
+	ret = set_sve(child, &vec_types[0], sve);
+	ksft_test_result(ret == 0, "FPSIMD write via SVE\n");
+	if (ret) {
+		ksft_test_result_skip("Verify FPSIMD write via SVE\n");
+		goto out;
+	}
+
+	/* Verify via the FPSIMD regset */
+	if (get_fpsimd(child, &new_fpsimd)) {
+		ksft_test_result_skip("Verify FPSIMD write via SVE\n");
+		goto out;
+	}
+	ksft_test_result(memcmp(fpsimd, &new_fpsimd, sizeof(*fpsimd)) == 0,
+			 "Verify FPSIMD write via SVE\n");
+
+out:
+	free(svebuf);
+}
+
 /* Validate attempting to set SVE data and read SVE data */
 static void ptrace_set_sve_get_sve_data(pid_t child,
 					const struct vec_type *type,
@@ -810,6 +862,15 @@ static int do_parent(pid_t child)
 		}
 	}
 
+	/* We support SVE writes of FPSMID format on SME only systems */
+	if (!(getauxval(AT_HWCAP) & HWCAP_SVE) &&
+	    (getauxval(AT_HWCAP2) & HWCAP2_SME)) {
+		ptrace_sve_fpsimd_no_sve(child);
+	} else {
+		ksft_test_result_skip("FPSIMD write via SVE\n");
+		ksft_test_result_skip("Verify FPSIMD write via SVE\n");
+	}
+
 	ret = EXIT_SUCCESS;
 
 error:

-- 
2.39.5