linux-kernel - [PATCH 3/3] perf/x86/intel: Fold current_vcpu check into KVM's PT intr handler

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Message-Id: <20210823193709.55886-4-seanjc@google.com>
Date:   Mon, 23 Aug 2021 12:37:09 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Artem Kashkanov <artem.kashkanov@...el.com>
Subject: [PATCH 3/3] perf/x86/intel: Fold current_vcpu check into KVM's PT
 intr handler

Move the check for a non-NULL current_vcpu into KVM's PT intr handler
instead of relying on the caller to perform the check.  In addition to
ensuring KVM's handler won't dereference a NULL pointer (and making it
obvious that it can't), this avoids a reptoline when KVM is configured to
run PT in "system mode", in which case handle_intel_pt_intr will be NULL.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/events/intel/core.c | 7 +++----
 arch/x86/kvm/pmu.h           | 2 +-
 arch/x86/kvm/x86.c           | 6 +++++-
 include/linux/perf_event.h   | 2 +-
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index fca7a6e2242f..060f1f1ebe15 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2852,10 +2852,9 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
 	 */
 	if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
 		handled++;
-		if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() &&
-			perf_guest_cbs->handle_intel_pt_intr))
-			perf_guest_cbs->handle_intel_pt_intr();
-		else
+		if (likely(!perf_guest_cbs ||
+			   !perf_guest_cbs->handle_intel_pt_intr ||
+			   perf_guest_cbs->handle_intel_pt_intr()))
 			intel_pt_interrupt();
 	}
 
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index b06dbbd7eeeb..4e8a38eca72b 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -41,7 +41,7 @@ struct kvm_pmu_ops {
 	void (*reset)(struct kvm_vcpu *vcpu);
 	void (*deliver_pmi)(struct kvm_vcpu *vcpu);
 	void (*cleanup)(struct kvm_vcpu *vcpu);
-	void (*handle_intel_pt_intr)(void);
+	int (*handle_intel_pt_intr)(void);
 };
 
 static inline u64 pmc_bitmask(struct kvm_pmc *pmc)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b5ade47dad9c..3f289192f25f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8292,13 +8292,17 @@ static unsigned long kvm_get_guest_ip(void)
 	return ip;
 }
 
-static void kvm_handle_intel_pt_intr(void)
+static int kvm_handle_intel_pt_intr(void)
 {
 	struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
 
+	if (!vcpu)
+		return -ENXIO;
+
 	kvm_make_request(KVM_REQ_PMI, vcpu);
 	__set_bit(MSR_CORE_PERF_GLOBAL_OVF_CTRL_TRACE_TOPA_PMI_BIT,
 			(unsigned long *)&vcpu->arch.pmu.global_status);
+	return 0;
 }
 
 static struct perf_guest_info_callbacks kvm_guest_cbs = {
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2d510ad750ed..f812c2570285 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -30,7 +30,7 @@ struct perf_guest_info_callbacks {
 	int				(*is_in_guest)(void);
 	int				(*is_user_mode)(void);
 	unsigned long			(*get_guest_ip)(void);
-	void				(*handle_intel_pt_intr)(void);
+	int				(*handle_intel_pt_intr)(void);
 };
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-- 
2.33.0.rc2.250.ged5fa647cd-goog