[PATCH v2 9/9] KVM: mark requests that need synchronization

["Radim Krčmář" <rkrcmar@redhat.com>]

kvm_make_all_requests() provides a synchronization that waits until all
kicked VCPUs have acknowledged the kick.  This is important for
KVM_REQ_MMU_RELOAD as it prevents freeing while lockless paging is
underway.

This patch adds the synchronization property into all requests that are
currently being used with kvm_make_all_requests() in order to preserve
the current behavior and only introduce a new framework.  Removing it
from requests where it is not necessary is left for future patches.

A question is whether this propertly isn't better expressed as a
function of the caller.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2: replaces [v1 1/6]
     Ugh, KVM_ARCH_REQ_WAIT_NO_WAKEUP looks a weird ...
---
 arch/arm/include/asm/kvm_host.h   |  2 +-
 arch/arm64/include/asm/kvm_host.h |  2 +-
 arch/x86/include/asm/kvm_host.h   |  6 +++---
 include/linux/kvm_host.h          |  8 ++++++--
 virt/kvm/kvm_main.c               | 16 +++++++++++++---
 5 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 1d48a4b65b86..2190a7ddd515 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -44,7 +44,7 @@
 #define KVM_MAX_VCPUS VGIC_V2_MAX_CPUS
 #endif
 
-#define KVM_REQ_VCPU_EXIT	KVM_ARCH_REQ_NO_WAKEUP(0)
+#define KVM_REQ_VCPU_EXIT	KVM_ARCH_REQ_WAIT_NO_WAKEUP(0)
 
 u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
 int __attribute_const__ kvm_target_cpu(void);
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index d3370b79660e..98f3d01ae91b 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -41,7 +41,7 @@
 
 #define KVM_VCPU_MAX_FEATURES 4
 
-#define KVM_REQ_VCPU_EXIT	KVM_ARCH_REQ_NO_WAKEUP(0)
+#define KVM_REQ_VCPU_EXIT	KVM_ARCH_REQ_WAIT_NO_WAKEUP(0)
 
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 15eb7d3837e3..77083d7e9540 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -61,10 +61,10 @@
 #define KVM_REQ_PMI			KVM_ARCH_REQ(11)
 #define KVM_REQ_SMI			KVM_ARCH_REQ(12)
 #define KVM_REQ_MASTERCLOCK_UPDATE	KVM_ARCH_REQ(13)
-#define KVM_REQ_MCLOCK_INPROGRESS	KVM_ARCH_REQ_NO_WAKEUP(14)
-#define KVM_REQ_SCAN_IOAPIC		KVM_ARCH_REQ_NO_WAKEUP(15)
+#define KVM_REQ_MCLOCK_INPROGRESS	KVM_ARCH_REQ_WAIT_NO_WAKEUP(14)
+#define KVM_REQ_SCAN_IOAPIC		KVM_ARCH_REQ_WAIT_NO_WAKEUP(15)
 #define KVM_REQ_GLOBAL_CLOCK_UPDATE	KVM_ARCH_REQ(16)
-#define KVM_REQ_APIC_PAGE_RELOAD	KVM_ARCH_REQ_NO_WAKEUP(17)
+#define KVM_REQ_APIC_PAGE_RELOAD	KVM_ARCH_REQ_WAIT_NO_WAKEUP(17)
 #define KVM_REQ_HV_CRASH		KVM_ARCH_REQ(18)
 #define KVM_REQ_IOAPIC_EOI_EXIT		KVM_ARCH_REQ(19)
 #define KVM_REQ_HV_RESET		KVM_ARCH_REQ(20)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 38cfe372918c..a668f33b20dc 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -117,12 +117,13 @@ static inline bool is_error_page(struct page *page)
 
 #define KVM_REQUEST_MASK           GENMASK(7,0)
 #define KVM_REQUEST_NO_WAKEUP      BIT(8)
+#define KVM_REQUEST_WAIT           BIT(9)
 /*
  * Architecture-independent vcpu->requests bit members
  * Bits 4-7 are reserved for more arch-independent bits.
  */
-#define KVM_REQ_TLB_FLUSH          (0 | KVM_REQUEST_NO_WAKEUP)
-#define KVM_REQ_MMU_RELOAD         (1 | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_TLB_FLUSH          (0 | KVM_REQUEST_NO_WAKEUP | KVM_REQUEST_WAIT)
+#define KVM_REQ_MMU_RELOAD         (1 | KVM_REQUEST_NO_WAKEUP | KVM_REQUEST_WAIT)
 #define KVM_REQ_PENDING_TIMER      2
 #define KVM_REQ_UNHALT             3
 #define KVM_REQUEST_ARCH_BASE      8
@@ -133,6 +134,9 @@ static inline bool is_error_page(struct page *page)
 })
 #define KVM_ARCH_REQ(nr)           KVM_ARCH_REQ_FLAGS(nr, 0)
 #define KVM_ARCH_REQ_NO_WAKEUP(nr) KVM_ARCH_REQ_FLAGS(nr, KVM_REQUEST_NO_WAKEUP)
+#define KVM_ARCH_REQ_WAIT(nr)      KVM_ARCH_REQ_FLAGS(nr, KVM_REQUEST_NO_WAKEUP)
+#define KVM_ARCH_REQ_WAIT_NO_WAKEUP(nr) \
+	KVM_ARCH_REQ_FLAGS(nr, KVM_REQUEST_NO_WAKEUP | KVM_REQUEST_WAIT)
 
 #define KVM_USERSPACE_IRQ_SOURCE_ID		0
 #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID	1
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 632f7b3e198c..dbf0410cd8b2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -165,6 +165,15 @@ void vcpu_put(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(vcpu_put);
 
+/* TODO: merge with kvm_arch_vcpu_should_kick */
+static bool kvm_should_kick_request(struct kvm_vcpu *vcpu, unsigned req)
+{
+	int mode = kvm_vcpu_exiting_guest_mode(vcpu);
+
+	return req & KVM_REQUEST_WAIT ?
+		mode != OUTSIDE_GUEST_MODE : mode == IN_GUEST_MODE;
+}
+
 static void ack_flush(void *_completed)
 {
 }
@@ -174,6 +183,7 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
 	int i, cpu, me;
 	cpumask_var_t cpus;
 	bool called = true;
+	bool wait = req & KVM_REQUEST_WAIT;
 	struct kvm_vcpu *vcpu;
 
 	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
@@ -187,13 +197,13 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
 			continue;
 
 		if (cpus != NULL && cpu != -1 && cpu != me &&
-		      kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
+		    kvm_should_kick_request(vcpu, req))
 			cpumask_set_cpu(cpu, cpus);
 	}
 	if (unlikely(cpus == NULL))
-		smp_call_function_many(cpu_online_mask, ack_flush, NULL, 1);
+		smp_call_function_many(cpu_online_mask, ack_flush, NULL, wait);
 	else if (!cpumask_empty(cpus))
-		smp_call_function_many(cpus, ack_flush, NULL, 1);
+		smp_call_function_many(cpus, ack_flush, NULL, wait);
 	else
 		called = false;
 	put_cpu();
-- 
2.12.2