[PATCH v6 04/28] arm64/fpsimd: Determine maximum virtualisable SME vector length

[Mark Brown <broonie@kernel.org>]

As with SVE we can only virtualise SME vector lengths that are supported by
all CPUs in the system, implement similar checks to those for SVE. Since
unlike SVE there are no specific vector lengths that are architecturally
required the handling is subtly different, we report a system where this
happens with a maximum vector length of -1.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/fpsimd.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index de2897d6208c..fbc586813f6a 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1244,7 +1244,8 @@ void cpu_enable_sme(const struct arm64_cpu_capabilities *__always_unused p)
 void __init sme_setup(void)
 {
 	struct vl_info *info = &vl_info[ARM64_VEC_SME];
-	int min_bit, max_bit;
+	DECLARE_BITMAP(tmp_map, SVE_VQ_MAX);
+	int min_bit, max_bit, b;
 
 	if (!system_supports_sme())
 		return;
@@ -1274,12 +1275,32 @@ void __init sme_setup(void)
 	 */
 	set_sme_default_vl(find_supported_vector_length(ARM64_VEC_SME, 32));
 
+	bitmap_andnot(tmp_map, info->vq_partial_map, info->vq_map,
+		      SVE_VQ_MAX);
+
+	b = find_last_bit(tmp_map, SVE_VQ_MAX);
+	if (b >= SVE_VQ_MAX)
+		/* All VLs virtualisable */
+		info->max_virtualisable_vl = SVE_VQ_MAX;
+	else if (b == SVE_VQ_MAX - 1)
+		/* No virtualisable VLs */
+		info->max_virtualisable_vl = -1;
+	else
+		info->max_virtualisable_vl = sve_vl_from_vq(__bit_to_vq(b +  1));
+
+	if (info->max_virtualisable_vl > info->max_vl)
+		info->max_virtualisable_vl = info->max_vl;
+
 	pr_info("SME: minimum available vector length %u bytes per vector\n",
 		info->min_vl);
 	pr_info("SME: maximum available vector length %u bytes per vector\n",
 		info->max_vl);
 	pr_info("SME: default vector length %u bytes per vector\n",
 		get_sme_default_vl());
+
+	/* KVM decides whether to support mismatched systems. Just warn here: */
+	if (info->max_virtualisable_vl < info->max_vl)
+		pr_warn("SME: unvirtualisable vector lengths present\n");
 }
 
 void sme_suspend_exit(void)

-- 
2.39.5