arm64/sme: Restore SMCR_EL1.EZT0 on exit from suspend

The fields in SMCR_EL1 reset to an architecturally UNKNOWN value. Since we
do not otherwise manage the traps configured in this register at runtime we
need to reconfigure them after a suspend in case nothing else was kind
enough to preserve them for us. Do so for SMCR_EL1.EZT0.

Fixes: d4913ee ("arm64/sme: Add basic enumeration for SME2")
Reported-by: Jackson Cooper-Driver <Jackson.Cooper-Driver@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240213-arm64-sme-resume-v3-2-17e05e493471@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

Author: broonie

arch/arm64/kernel/fpsimd.c

@@ -1320,6 +1320,8 @@ void sme_suspend_exit(void)
 
 	if (system_supports_fa64())
 		smcr |= SMCR_ELx_FA64;
+	if (system_supports_sme2())
+		smcr |= SMCR_ELx_EZT0;
 
 	write_sysreg_s(smcr, SYS_SMCR_EL1);
 	write_sysreg_s(0, SYS_SMPRI_EL1);