From efad60e4605721b829a49bcaa6afc517a80a7247 Mon Sep 17 00:00:00 2001 From: Alexandru Elisei Date: Tue, 2 Sep 2025 14:08:32 +0100 Subject: [PATCH] KVM: arm64: Initialize PMSCR_EL1 when in VHE According to the pseudocode for StatisticalProfilingEnabled() from Arm DDI0487L.b, PMSCR_EL1 controls profiling at EL1 and EL0: - PMSCR_EL1.E1SPE controls profiling at EL1. - PMSCR_EL1.E0SPE controls profiling at EL0 if HCR_EL2.TGE=0. These two fields reset to UNKNOWN values. When KVM runs in VHE mode and profiling is enabled in the host, before entering a guest, KVM does not touch any of the SPE registers, leaving the buffer enabled, and it clears HCR_EL2.TGE. As a result, depending on the reset value for the E1SPE and E0SPE fields, KVM might unintentionally profile a guest. Make the behaviour consistent and predictable by clearing PMSCR_EL1 when KVM initialises the host debug configuration. Note that this is not a problem for nVHE, because KVM clears PMSCR_EL1.{E1SPE,E0SPE} before entering the guest. Signed-off-by: Alexandru Elisei Link: https://lore.kernel.org/r/20250902130833.338216-2-alexandru.elisei@arm.com Signed-off-by: Oliver Upton --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/arm.c | 4 +++- arch/arm64/kvm/debug.c | 7 +++++++ 3 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 2b07f0a27a7d8..0ee4f6fa3a172 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -1369,6 +1369,7 @@ static inline bool kvm_system_needs_idmapped_vectors(void) } void kvm_init_host_debug_data(void); +void kvm_debug_init_vhe(void); void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu); void kvm_vcpu_put_debug(struct kvm_vcpu *vcpu); void kvm_debug_set_guest_ownership(struct kvm_vcpu *vcpu); diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 5bf101c869c9a..bd6b6a620a09c 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -2113,8 +2113,10 @@ static void cpu_hyp_init_features(void) { cpu_set_hyp_vector(); - if (is_kernel_in_hyp_mode()) + if (is_kernel_in_hyp_mode()) { kvm_timer_init_vhe(); + kvm_debug_init_vhe(); + } if (vgic_present) kvm_vgic_init_cpu_hardware(); diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c index 381382c19fe47..fee6e882490ab 100644 --- a/arch/arm64/kvm/debug.c +++ b/arch/arm64/kvm/debug.c @@ -96,6 +96,13 @@ 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))) + write_sysreg_el1(0, SYS_PMSCR); +} + /* * Configures the 'external' MDSCR_EL1 value for the guest, i.e. when the host * has taken over MDSCR_EL1. -- 2.47.3