arm64/sve: Remove ZCR pseudo register from cpufeature code

For reasons that are not currently apparent during cpufeature enumeration
we maintain a pseudo register for ZCR which records the maximum supported
vector length using the value that would be written to ZCR_EL1.LEN to
configure it. This is not exposed to userspace and is not sufficient for
detecting unsupportable configurations, we need the more detailed checks in
vec_update_vq_map() for that since we can't cope with missing vector
lengths on late CPUs and KVM requires an exactly matching set of supported
vector lengths as EL1 can enumerate VLs directly with the hardware.

Remove the code, replacing the usage in sve_setup() with a query of the
vq_map.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230913-arm64-vec-len-cpufeature-v1-1-cc69b0600a8a@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 3 insertions, 32 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 91e44ac7150f..35bf40c2f972 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1170,32 +1170,12 @@ void sve_kernel_enable(const struct arm64_cpu_capabilities *__always_unused p)
 	isb();
 }
 
-/*
- * Read the pseudo-ZCR used by cpufeatures to identify the supported SVE
- * vector length.
- *
- * Use only if SVE is present.
- * This function clobbers the SVE vector length.
- */
-u64 read_zcr_features(void)
-{
-	/*
-	 * Set the maximum possible VL, and write zeroes to all other
-	 * bits to see if they stick.
-	 */
-	sve_kernel_enable(NULL);
-	write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL1);
-
-	/* Return LEN value that would be written to get the maximum VL */
-	return sve_vq_from_vl(sve_get_vl()) - 1;
-}
-
 void __init sve_setup(void)
 {
 	struct vl_info *info = &vl_info[ARM64_VEC_SVE];
-	u64 zcr;
 	DECLARE_BITMAP(tmp_map, SVE_VQ_MAX);
 	unsigned long b;
+	int max_bit;
 
 	if (!system_supports_sve())
 		return;
@@ -1208,17 +1188,8 @@ void __init sve_setup(void)
 	if (WARN_ON(!test_bit(__vq_to_bit(SVE_VQ_MIN), info->vq_map)))
 		set_bit(__vq_to_bit(SVE_VQ_MIN), info->vq_map);
 
-	zcr = read_sanitised_ftr_reg(SYS_ZCR_EL1);
-	info->max_vl = sve_vl_from_vq((zcr & ZCR_ELx_LEN_MASK) + 1);
-
-	/*
-	 * Sanity-check that the max VL we determined through CPU features
-	 * corresponds properly to sve_vq_map.  If not, do our best:
-	 */
-	if (WARN_ON(info->max_vl != find_supported_vector_length(ARM64_VEC_SVE,
-								 info->max_vl)))
-		info->max_vl = find_supported_vector_length(ARM64_VEC_SVE,
-							    info->max_vl);
+	max_bit = find_first_bit(info->vq_map, SVE_VQ_MAX);
+	info->max_vl = sve_vl_from_vq(__bit_to_vq(max_bit));
 
 	/*
 	 * For the default VL, pick the maximum supported value <= 64.