KVM: mark requests that need synchronization

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.
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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	(8 | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_VCPU_EXIT	(8 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 
 u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
 int __attribute_const__ kvm_target_cpu(void);

arch/arm64/include/asm/kvm_host.h

@@ -41,7 +41,7 @@
 
 #define KVM_VCPU_MAX_FEATURES 4
 
-#define KVM_REQ_VCPU_EXIT	(8 | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_VCPU_EXIT	(8 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);

arch/x86/include/asm/kvm_host.h

@@ -61,10 +61,10 @@
 #define KVM_REQ_PMI               19
 #define KVM_REQ_SMI               20
 #define KVM_REQ_MASTERCLOCK_UPDATE 21
-#define KVM_REQ_MCLOCK_INPROGRESS (22 | KVM_REQUEST_NO_WAKEUP)
-#define KVM_REQ_SCAN_IOAPIC       (23 | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_MCLOCK_INPROGRESS (22 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_SCAN_IOAPIC       (23 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_GLOBAL_CLOCK_UPDATE 24
-#define KVM_REQ_APIC_PAGE_RELOAD  (25 | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_APIC_PAGE_RELOAD  (25 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_HV_CRASH          26
 #define KVM_REQ_IOAPIC_EOI_EXIT   27
 #define KVM_REQ_HV_RESET          28

include/linux/kvm_host.h

@@ -117,14 +117,15 @@ 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_PENDING_TIMER      2
-#define KVM_REQ_UNHALT             3
+#define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_PENDING_TIMER     2
+#define KVM_REQ_UNHALT            3
 
 #define KVM_USERSPACE_IRQ_SOURCE_ID		0
 #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID	1

virt/kvm/kvm_main.c

@@ -165,6 +165,24 @@ void vcpu_put(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(vcpu_put);
 
+/* TODO: merge with kvm_arch_vcpu_should_kick */
+static bool kvm_request_needs_ipi(struct kvm_vcpu *vcpu, unsigned req)
+{
+	int mode = kvm_vcpu_exiting_guest_mode(vcpu);
+
+	/*
+	 * We need to wait for the VCPU to reenable interrupts and get out of
+	 * READING_SHADOW_PAGE_TABLES mode.
+	 */
+	if (req & KVM_REQUEST_WAIT)
+		return mode != OUTSIDE_GUEST_MODE;
+
+	/*
+	 * Need to kick a running VCPU, but otherwise there is nothing to do.
+	 */
+	return mode == IN_GUEST_MODE;
+}
+
 static void ack_flush(void *_completed)
 {
 }
@@ -174,6 +192,7 @@ 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 +206,13 @@ 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_request_needs_ipi(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();