KVM: Halt vcpu if page it tries to access is swapped out

If a guest accesses swapped out memory do not swap it in from vcpu thread
context. Schedule work to do swapping and put vcpu into halted state
instead.

Interrupts will still be delivered to the guest and if interrupt will
cause reschedule guest will continue to run another task.

[avi: remove call to get_user_pages_noio(), nacked by Linus; this
      makes everything synchrnous again]

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 51 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index fbb04aee8301..4ab04de5a76a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -18,9 +18,11 @@
  *
  */
 
+#include "irq.h"
 #include "mmu.h"
 #include "x86.h"
 #include "kvm_cache_regs.h"
+#include "x86.h"
 
 #include <linux/kvm_host.h>
 #include <linux/types.h>
@@ -2587,6 +2589,50 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
 			     error_code & PFERR_WRITE_MASK, gfn);
 }
 
+int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
+{
+	struct kvm_arch_async_pf arch;
+	arch.gfn = gfn;
+
+	return kvm_setup_async_pf(vcpu, gva, gfn, &arch);
+}
+
+static bool can_do_async_pf(struct kvm_vcpu *vcpu)
+{
+	if (unlikely(!irqchip_in_kernel(vcpu->kvm) ||
+		     kvm_event_needs_reinjection(vcpu)))
+		return false;
+
+	return kvm_x86_ops->interrupt_allowed(vcpu);
+}
+
+static bool try_async_pf(struct kvm_vcpu *vcpu, gfn_t gfn, gva_t gva,
+			 pfn_t *pfn)
+{
+	bool async;
+
+	*pfn = gfn_to_pfn_async(vcpu->kvm, gfn, &async);
+
+	if (!async)
+		return false; /* *pfn has correct page already */
+
+	put_page(pfn_to_page(*pfn));
+
+	if (can_do_async_pf(vcpu)) {
+		trace_kvm_try_async_get_page(async, *pfn);
+		if (kvm_find_async_pf_gfn(vcpu, gfn)) {
+			trace_kvm_async_pf_doublefault(gva, gfn);
+			kvm_make_request(KVM_REQ_APF_HALT, vcpu);
+			return true;
+		} else if (kvm_arch_setup_async_pf(vcpu, gva, gfn))
+			return true;
+	}
+
+	*pfn = gfn_to_pfn(vcpu->kvm, gfn);
+
+	return false;
+}
+
 static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
 				u32 error_code)
 {
@@ -2609,7 +2655,11 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
-	pfn = gfn_to_pfn(vcpu->kvm, gfn);
+
+	if (try_async_pf(vcpu, gfn, gpa, &pfn))
+		return 0;
+
+	/* mmio */
 	if (is_error_pfn(pfn))
 		return kvm_handle_bad_page(vcpu->kvm, gfn, pfn);
 	spin_lock(&vcpu->kvm->mmu_lock);