linux-kernel - [PATCH v7 07/12] KVM: arm64: arm_spe: Give SPE enabled state to KVM

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Message-Id: <20241112103717.589952-8-james.clark@linaro.org>
Date: Tue, 12 Nov 2024 10:37:06 +0000
From: James Clark <james.clark@...aro.org>
To: suzuki.poulose@....com,
	oliver.upton@...ux.dev,
	coresight@...ts.linaro.org,
	kvmarm@...ts.linux.dev
Cc: James Clark <james.clark@...aro.org>,
	Marc Zyngier <maz@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mike Leach <mike.leach@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Fuad Tabba <tabba@...gle.com>,
	James Morse <james.morse@....com>,
	Shiqi Liu <shiqiliu@...t.edu.cn>,
	Mark Brown <broonie@...nel.org>,
	Raghavendra Rao Ananta <rananta@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v7 07/12] KVM: arm64: arm_spe: Give SPE enabled state to KVM

Currently in nVHE, KVM has to check if SPE is enabled on every guest
switch even if it was never used. Because it's a debug feature and is
more likely to not be used than used, give KVM the SPE buffer status to
allow a much simpler and faster do-nothing path in the hyp.

This is always called with preemption disabled except for probe/hotplug
which gets wrapped with preempt_disable().

Signed-off-by: James Clark <james.clark@...aro.org>
---
 arch/arm64/include/asm/kvm_host.h |  6 ++++++
 arch/arm64/kvm/debug.c            | 29 +++++++++++++++++++++++++++++
 drivers/perf/arm_spe_pmu.c        | 13 +++++++++++--
 3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 5dfc3f4f74b2..7f1e32d40f0c 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -641,6 +641,8 @@ struct kvm_host_data {
 	struct {
 		/* Host CPU features, set at init */
 		u8 feats;
+		/* Host CPU state */
+		u8 state;
 	} flags;
 
 	/*
@@ -941,6 +943,8 @@ struct kvm_vcpu_arch {
 #define HOST_FEAT_HAS_TRBE	__kvm_single_flag(feats, BIT(1))
 /* CPU has Feat_TRF */
 #define HOST_FEAT_HAS_TRF	__kvm_single_flag(feats, BIT(2))
+/* PMBLIMITR_EL1_E is set (SPE profiling buffer enabled) */
+#define HOST_STATE_SPE_EN	__kvm_single_flag(state, BIT(0))
 
 /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
 #define vcpu_sve_pffr(vcpu) (kern_hyp_va((vcpu)->arch.sve_state) +	\
@@ -1382,6 +1386,7 @@ static inline bool kvm_pmu_counter_deferred(struct perf_event_attr *attr)
 void kvm_set_pmu_events(u64 set, struct perf_event_attr *attr);
 void kvm_clr_pmu_events(u64 clr);
 bool kvm_set_pmuserenr(u64 val);
+void kvm_set_pmblimitr(u64 pmblimitr);
 #else
 static inline void kvm_set_pmu_events(u64 set, struct perf_event_attr *attr) {}
 static inline void kvm_clr_pmu_events(u64 clr) {}
@@ -1389,6 +1394,7 @@ static inline bool kvm_set_pmuserenr(u64 val)
 {
 	return false;
 }
+static inline void kvm_set_pmblimitr(u64 pmblimitr) {}
 #endif
 
 void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index fb41ef5d9db9..ed3b4d057c52 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -335,3 +335,32 @@ void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 		}
 	}
 }
+
+static bool kvm_arm_skip_trace_state(void)
+{
+	/* pKVM hyp finds out the state for itself */
+	if (is_protected_kvm_enabled())
+		return true;
+
+	/* Make sure state gets there in one piece */
+	if (WARN_ON_ONCE(preemptible()))
+		return true;
+
+	return false;
+}
+
+void kvm_set_pmblimitr(u64 pmblimitr)
+{
+	/* Only read in nVHE */
+	if (has_vhe())
+		return;
+
+	if (kvm_arm_skip_trace_state())
+		return;
+
+	if (pmblimitr & PMBLIMITR_EL1_E)
+		host_data_set_flag(HOST_STATE_SPE_EN);
+	else
+		host_data_clear_flag(HOST_STATE_SPE_EN);
+}
+EXPORT_SYMBOL_GPL(kvm_set_pmblimitr);
diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index 3569050f9cf3..6a79df363aa6 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c
@@ -23,6 +23,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/kernel.h>
+#include <linux/kvm_host.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -496,6 +497,12 @@ static u64 arm_spe_pmu_next_off(struct perf_output_handle *handle)
 	return limit;
 }
 
+static void arm_spe_write_pmblimitr(u64 val)
+{
+	write_sysreg_s(val, SYS_PMBLIMITR_EL1);
+	kvm_set_pmblimitr(val);
+}
+
 static void arm_spe_perf_aux_output_begin(struct perf_output_handle *handle,
 					  struct perf_event *event)
 {
@@ -524,7 +531,7 @@ static void arm_spe_perf_aux_output_begin(struct perf_output_handle *handle,
 	write_sysreg_s(base, SYS_PMBPTR_EL1);
 
 out_write_limit:
-	write_sysreg_s(limit, SYS_PMBLIMITR_EL1);
+	arm_spe_write_pmblimitr(limit);
 }
 
 static void arm_spe_perf_aux_output_end(struct perf_output_handle *handle)
@@ -552,7 +559,7 @@ static void arm_spe_pmu_disable_and_drain_local(void)
 	dsb(nsh);
 
 	/* Disable the profiling buffer */
-	write_sysreg_s(0, SYS_PMBLIMITR_EL1);
+	arm_spe_write_pmblimitr(0);
 	isb();
 }
 
@@ -1095,7 +1102,9 @@ static void __arm_spe_pmu_reset_local(void)
 	 * This is probably overkill, as we have no idea where we're
 	 * draining any buffered data to...
 	 */
+	preempt_disable();
 	arm_spe_pmu_disable_and_drain_local();
+	preempt_enable();
 
 	/* Reset the buffer base pointer */
 	write_sysreg_s(0, SYS_PMBPTR_EL1);
-- 
2.34.1