linux-kernel - [PATCH v2 14/43] KVM: Split out a kvm_vcpu_block() helper from kvm_vcpu

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Message-Id: <20211009021236.4122790-15-seanjc@google.com>
Date:   Fri,  8 Oct 2021 19:12:07 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        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-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: [PATCH v2 14/43] KVM: Split out a kvm_vcpu_block() helper from kvm_vcpu_halt()

Factor out the "block" part of kvm_vcpu_halt() so that x86 can emulate
non-halt wait/sleep/block conditions that should not be subjected to
halt-polling.

No functional change intended.

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
Reviewed-by: David Matlack <dmatlack@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 52 +++++++++++++++++++++++++++-------------
 2 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c2ea4004553a..2d837e06eeec 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -968,6 +968,7 @@ void kvm_sigset_activate(struct kvm_vcpu *vcpu);
 void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
 
 void kvm_vcpu_halt(struct kvm_vcpu *vcpu);
+bool kvm_vcpu_block(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);
 bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c13bf3367fda..42894ff7c474 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3201,6 +3201,35 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
+/*
+ * Block the vCPU until the vCPU is runnable, an event arrives, or a signal is
+ * pending.  This is mostly used when halting a vCPU, but may also be used
+ * directly for other vCPU non-runnable states, e.g. x86's Wait-For-SIPI.
+ */
+bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
+{
+	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
+	bool waited = false;
+
+	kvm_arch_vcpu_blocking(vcpu);
+
+	prepare_to_rcuwait(wait);
+	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (kvm_vcpu_check_block(vcpu) < 0)
+			break;
+
+		waited = true;
+		schedule();
+	}
+	finish_rcuwait(wait);
+
+	kvm_arch_vcpu_unblocking(vcpu);
+
+	return waited;
+}
+
 static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
 					  ktime_t end, bool success)
 {
@@ -3223,9 +3252,14 @@ static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
 	}
 }
 
+/*
+ * Emulate a vCPU halt condition, e.g. HLT on x86, WFI on arm, etc...  If halt
+ * polling is enabled, busy wait for a short time before blocking to avoid the
+ * expensive block+unblock sequence if a wake event arrives soon after the vCPU
+ * is halted.
+ */
 void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
 {
-	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
 	bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
 	bool do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
 	ktime_t start, cur, poll_end;
@@ -3248,21 +3282,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
 		} while (kvm_vcpu_can_poll(cur, stop));
 	}
 
-	kvm_arch_vcpu_blocking(vcpu);
-
-	prepare_to_rcuwait(wait);
-	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-
-		if (kvm_vcpu_check_block(vcpu) < 0)
-			break;
-
-		waited = true;
-		schedule();
-	}
-	finish_rcuwait(wait);
-
-	kvm_arch_vcpu_unblocking(vcpu);
+	waited = kvm_vcpu_block(vcpu);
 
 	cur = ktime_get();
 	if (waited) {
-- 
2.33.0.882.g93a45727a2-goog