[SRU][Q][PATCH 1/1] KVM: arm64: Guard PMSCR_EL1 initialization with SPE presence check

[Edoardo Canepa]

From: Mukesh Ojha <mukesh.ojha at oss.qualcomm.com>

BugLink: https://bugs.launchpad.net/bugs/2129770

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 <mukesh.ojha at oss.qualcomm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
(cherry picked from commit c35dd838666d47de2848639234ec32e3ba22b49f)
Signed-off-by: Edoardo Canepa <edoardo.canepa at canonical.com>
---
 arch/arm64/kvm/debug.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index e027d9c32b0d..1f018decf8ff 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -15,6 +15,12 @@
 #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
  *
@@ -74,13 +80,12 @@ void kvm_init_host_debug_data(void)
 	*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))
 		host_data_set_flag(HAS_BRBE);
@@ -99,7 +104,7 @@ void kvm_init_host_debug_data(void)
 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);
 }
 
-- 
2.51.0