KVM: arm64: Guard PMSCR_EL1 initialization with SPE presence check

Commit efad60e46057 ("KVM: arm64: Initialize PMSCR_EL1 when in VHE")
does not perform sufficient check before initializing PMSCR_EL1 to 0
when running in VHE mode. On some platforms, this causes the system to
hang during boot, as EL3 has not delegated access to the Profiling
Buffer to the Non-secure world, nor does it reinject an UNDEF on sysreg
trap.

To avoid this issue, restrict the PMSCR_EL1 initialization to CPUs that
support Statistical Profiling Extension (FEAT_SPE) and have the
Profiling Buffer accessible in Non-secure EL1. This is determined via a
new helper `cpu_has_spe()` which checks both PMSVer and PMBIDR_EL1.P.

This ensures the initialization only affects CPUs where SPE is
implemented and usable, preventing boot failures on platforms where SPE
is not properly configured.

Fixes: efad60e46057 ("KVM: arm64: Initialize PMSCR_EL1 when in VHE")
Signed-off-by: Mukesh Ojha <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

arch/arm64/kvm/debug.c

···
 #include <asm/kvm_arm.h>
 #include <asm/kvm_emulate.h>
 
+static int cpu_has_spe(u64 dfr0)
+{
+	return cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMSVer_SHIFT) &&
+	       !(read_sysreg_s(SYS_PMBIDR_EL1) & PMBIDR_EL1_P);
+}
+
 /**
  * kvm_arm_setup_mdcr_el2 - configure vcpu mdcr_el2 value
  *
···
 	*host_data_ptr(debug_brps) = SYS_FIELD_GET(ID_AA64DFR0_EL1, BRPs, dfr0);
 	*host_data_ptr(debug_wrps) = SYS_FIELD_GET(ID_AA64DFR0_EL1, WRPs, dfr0);
 
+	if (cpu_has_spe(dfr0))
+		host_data_set_flag(HAS_SPE);
+
 	if (has_vhe())
 		return;
-
-	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMSVer_SHIFT) &&
-	    !(read_sysreg_s(SYS_PMBIDR_EL1) & PMBIDR_EL1_P))
-		host_data_set_flag(HAS_SPE);
 
 	/* Check if we have BRBE implemented and available at the host */
 	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_BRBE_SHIFT))
···
 void kvm_debug_init_vhe(void)
 {
 	/* Clear PMSCR_EL1.E{0,1}SPE which reset to UNKNOWN values. */
-	if (SYS_FIELD_GET(ID_AA64DFR0_EL1, PMSVer, read_sysreg(id_aa64dfr0_el1)))
+	if (host_data_test_flag(HAS_SPE))
 		write_sysreg_el1(0, SYS_PMSCR);
 }