Re: [PATCH v3 10/16] KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu variable

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On 22/09/21 02:05, Sean Christopherson wrote:
Use the generic kvm_running_vcpu plus a new 'handling_intr_from_guest'
variable in kvm_arch_vcpu instead of the semi-redundant current_vcpu.
kvm_before/after_interrupt() must be called while the vCPU is loaded,
(which protects against preemption), thus kvm_running_vcpu is guaranteed
to be non-NULL when handling_intr_from_guest is non-zero.

Switching to kvm_get_running_vcpu() will allows moving KVM's perf
callbacks to generic code, and the new flag will be used in a future
patch to more precisely identify the "NMI from guest" case.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
  arch/x86/include/asm/kvm_host.h |  3 +--
  arch/x86/kvm/pmu.c              |  2 +-
  arch/x86/kvm/x86.c              | 21 ++++++++++++---------
  arch/x86/kvm/x86.h              | 10 ++++++----
  4 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1080166fc0cf..2d86a2dfc775 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -763,6 +763,7 @@ struct kvm_vcpu_arch {
  	unsigned nmi_pending; /* NMI queued after currently running handler */
  	bool nmi_injected;    /* Trying to inject an NMI this entry */
  	bool smi_pending;    /* SMI queued after currently running handler */
+	u8 handling_intr_from_guest;
struct kvm_mtrr mtrr_state;
  	u64 pat;
@@ -1874,8 +1875,6 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu);
  int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err);
  void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu);
-unsigned int kvm_guest_state(void);
-
  void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
  				     u32 size);
  bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 5b68d4188de0..eef48258e50f 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -87,7 +87,7 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event,
  		 * woken up. So we should wake it, but this is impossible from
  		 * NMI context. Do it from irq work instead.
  		 */
-		if (!kvm_guest_state())
+		if (!kvm_handling_nmi_from_guest(pmc->vcpu))
  			irq_work_queue(&pmc_to_pmu(pmc)->irq_work);
  		else
  			kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6cc66466f301..24a6faa07442 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8264,15 +8264,17 @@ static void kvm_timer_init(void)
  			  kvmclock_cpu_online, kvmclock_cpu_down_prep);
  }
-DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
-EXPORT_PER_CPU_SYMBOL_GPL(current_vcpu);
+static inline bool kvm_pmi_in_guest(struct kvm_vcpu *vcpu)
+{
+	return vcpu && vcpu->arch.handling_intr_from_guest;
+}
-unsigned int kvm_guest_state(void)
+static unsigned int kvm_guest_state(void)
  {
-	struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
+	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
  	unsigned int state;
- if (!vcpu)
+	if (!kvm_pmi_in_guest(vcpu))
  		return 0;
state = PERF_GUEST_ACTIVE;
@@ -8284,9 +8286,10 @@ unsigned int kvm_guest_state(void)
static unsigned long kvm_guest_get_ip(void)
  {
-	struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
+	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
- if (WARN_ON_ONCE(!vcpu))
+	/* Retrieving the IP must be guarded by a call to kvm_guest_state(). */
+	if (WARN_ON_ONCE(!kvm_pmi_in_guest(vcpu)))
  		return 0;
return kvm_rip_read(vcpu);
@@ -8294,10 +8297,10 @@ static unsigned long kvm_guest_get_ip(void)
static unsigned int kvm_handle_intel_pt_intr(void)
  {
-	struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
+	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
/* '0' on failure so that the !PT case can use a RET0 static call. */
-	if (!vcpu)
+	if (!kvm_pmi_in_guest(vcpu))
  		return 0;
kvm_make_request(KVM_REQ_PMI, vcpu);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 7d66d63dc55a..a9c107e7c907 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -387,18 +387,20 @@ static inline bool kvm_cstate_in_guest(struct kvm *kvm)
  	return kvm->arch.cstate_in_guest;
  }
-DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu);
-
  static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu)
  {
-	__this_cpu_write(current_vcpu, vcpu);
+	WRITE_ONCE(vcpu->arch.handling_intr_from_guest, 1);
  }
static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
  {
-	__this_cpu_write(current_vcpu, NULL);
+	WRITE_ONCE(vcpu->arch.handling_intr_from_guest, 0);
  }
+static inline bool kvm_handling_nmi_from_guest(struct kvm_vcpu *vcpu)
+{
+	return !!vcpu->arch.handling_intr_from_guest;
+}
static inline bool kvm_pat_valid(u64 data)
  {


Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

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