[PATCH V17 6/9] KVM: arm64: nvhe: Disable branch generation in nVHE guests

[Anshuman Khandual]

Disable the BRBE before we enter the guest, saving the status and enable it
back once we get out of the guest. This avoids capturing branch records in
the guest kernel or userspace, which would be confusing the host samples.

Cc: Marc Zyngier <maz at kernel.org>
Cc: Oliver Upton <oliver.upton at linux.dev>
Cc: James Morse <james.morse at arm.com>
Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: kvmarm at lists.linux.dev
Cc: linux-arm-kernel at lists.infradead.org
CC: linux-kernel at vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
----
Changes in V17:

- Dropped isb() call sites in  __debug_[save|restore]_brbe()
- Changed to [read|write]_sysreg_el1() accessors in __debug_[save|restore]_brbe()

 arch/arm64/include/asm/kvm_host.h  |  5 ++++-
 arch/arm64/kvm/debug.c             |  5 +++++
 arch/arm64/kvm/hyp/nvhe/debug-sr.c | 31 ++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9e8a496fb284..a105bea8ecd0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -609,7 +609,7 @@ struct kvm_vcpu_arch {
 	u8 cflags;
 
 	/* Input flags to the hypervisor code, potentially cleared after use */
-	u8 iflags;
+	u16 iflags;
 
 	/* State flags for kernel bookkeeping, unused by the hypervisor code */
 	u8 sflags;
@@ -650,6 +650,7 @@ struct kvm_vcpu_arch {
 		u64 pmscr_el1;
 		/* Self-hosted trace */
 		u64 trfcr_el1;
+		u64 brbcr_el1;
 	} host_debug_state;
 
 	/* VGIC state */
@@ -819,6 +820,8 @@ struct kvm_vcpu_arch {
 #define DEBUG_STATE_SAVE_TRBE	__vcpu_single_flag(iflags, BIT(6))
 /* vcpu running in HYP context */
 #define VCPU_HYP_CONTEXT	__vcpu_single_flag(iflags, BIT(7))
+/* Save BRBE context if active  */
+#define DEBUG_STATE_SAVE_BRBE	__vcpu_single_flag(iflags, BIT(8))
 
 /* SVE enabled for host EL0 */
 #define HOST_SVE_ENABLED	__vcpu_single_flag(sflags, BIT(0))
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index ce8886122ed3..8fa648943f0f 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -336,10 +336,15 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
 	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
 	    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
 		vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
+
+	/* Check if we have BRBE implemented and available at the host */
+	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_BRBE_SHIFT))
+		vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_BRBE);
 }
 
 void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
 {
 	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
 	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
+	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_BRBE);
 }
diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
index 7746ea507b6f..a6dec3646afc 100644
--- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
@@ -79,6 +79,32 @@ static void __debug_restore_trace(u64 trfcr_el1)
 	write_sysreg_el1(trfcr_el1, SYS_TRFCR);
 }
 
+static void __debug_save_brbe(u64 *brbcr_el1)
+{
+	*brbcr_el1 = 0;
+
+	/* Check if the BRBE is enabled */
+	if (!(read_sysreg_el1(SYS_BRBCR) & (BRBCR_ELx_E0BRE | BRBCR_ELx_ExBRE)))
+		return;
+
+	/*
+	 * Prohibit branch record generation while we are in guest.
+	 * Since access to BRBCR_EL1 is trapped, the guest can't
+	 * modify the filtering set by the host.
+	 */
+	*brbcr_el1 = read_sysreg_el1(SYS_BRBCR);
+	write_sysreg_el1(0, SYS_BRBCR);
+}
+
+static void __debug_restore_brbe(u64 brbcr_el1)
+{
+	if (!brbcr_el1)
+		return;
+
+	/* Restore BRBE controls */
+	write_sysreg_el1(brbcr_el1, SYS_BRBCR);
+}
+
 void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
 {
 	/* Disable and flush SPE data generation */
@@ -87,6 +113,9 @@ void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
 	/* Disable and flush Self-Hosted Trace generation */
 	if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
 		__debug_save_trace(&vcpu->arch.host_debug_state.trfcr_el1);
+	/* Disable BRBE branch records */
+	if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_BRBE))
+		__debug_save_brbe(&vcpu->arch.host_debug_state.brbcr_el1);
 }
 
 void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
@@ -100,6 +129,8 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
 		__debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
 	if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
 		__debug_restore_trace(vcpu->arch.host_debug_state.trfcr_el1);
+	if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_BRBE))
+		__debug_restore_brbe(vcpu->arch.host_debug_state.brbcr_el1);
 }
 
 void __debug_switch_to_host(struct kvm_vcpu *vcpu)
-- 
2.25.1