linux-kernel - [PATCH v3 6/7] KVM: mips, x86: do not rely on KVM_REQ

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Date:   Mon, 22 Aug 2022 13:06:58 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     mlevitsk@...hat.com, seanjc@...gle.com
Subject: [PATCH v3 6/7] KVM: mips, x86: do not rely on KVM_REQ_UNHALT

KVM_REQ_UNHALT is a weird request that simply reports the value of
kvm_arch_vcpu_runnable() on exit from kvm_vcpu_halt().  Only
MIPS and x86 are looking at it, the others just clear it.  Check
the state of the vCPU directly so that the request is handled
as a nop on all architectures.

No functional change intended, except for corner cases where an
event arrive immediately after a signal become pending or after
another similar host-side event.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/mips/kvm/emulate.c | 7 +++----
 arch/x86/kvm/x86.c      | 9 ++++++++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index b494d8d39290..1d7c56defe93 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -955,13 +955,12 @@ enum emulation_result kvm_mips_emul_wait(struct kvm_vcpu *vcpu)
 		kvm_vcpu_halt(vcpu);
 
 		/*
-		 * We we are runnable, then definitely go off to user space to
+		 * We are runnable, then definitely go off to user space to
 		 * check if any I/O interrupts are pending.
 		 */
-		if (kvm_check_request(KVM_REQ_UNHALT, vcpu)) {
-			kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+		if (kvm_arch_vcpu_runnable(vcpu))
 			vcpu->run->exit_reason = KVM_EXIT_IRQ_WINDOW_OPEN;
-		}
 	}
 
 	return EMULATE_DONE;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f901cd872b6d..66ae2f2cb618 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10633,7 +10633,14 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
 		if (hv_timer)
 			kvm_lapic_switch_to_hv_timer(vcpu);
 
-		if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
+		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+
+		/*
+		 * If the vCPU is not runnable, a signal or another host event
+		 * of some kind is pending; service it without changing the
+		 * the vCPU's activity state.
+		 */
+		if (!kvm_arch_vcpu_runnable(vcpu))
 			return 1;
 	}
 
-- 
2.31.1