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Commit e7df56e4 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: Remove extraneous guest entry on mmio read 



When emulating an mmio read, we actually emulate twice: once to determine
the physical address of the mmio, and, after we've exited to userspace to
get the mmio value, we emulate again to place the value in the result
register and update any flags.

But we don't really need to enter the guest again for that, only to take
an immediate vmexit.  So, if we detect that we're doing an mmio read,
emulate a single instruction before entering the guest again.

Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 94dfbdb3

drivers/kvm/kvm.h

+1 −0
Original line number Diff line number Diff line
@@ -310,6 +310,7 @@ struct kvm_vcpu { 
	int mmio_size;

	unsigned char mmio_data[8];

	gpa_t mmio_phys_addr;

	gva_t mmio_fault_cr2;

	struct kvm_pio_request pio;

	void *pio_data;

drivers/kvm/kvm_main.c

+13 −3
Original line number Diff line number Diff line
@@ -1186,6 +1186,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu, 
	int r;

	int cs_db, cs_l;



	vcpu->mmio_fault_cr2 = cr2;

	kvm_arch_ops->cache_regs(vcpu);



	kvm_arch_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
@@ -1804,13 +1805,22 @@ static int kvm_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
			r = complete_pio(vcpu);

			if (r)

				goto out;

		} else {

		} else if (!vcpu->mmio_is_write) {

			memcpy(vcpu->mmio_data, kvm_run->mmio.data, 8);

			vcpu->mmio_read_completed = 1;

			vcpu->mmio_needed = 0;

			r = emulate_instruction(vcpu, kvm_run,

					    vcpu->mmio_fault_cr2, 0);

			if (r == EMULATE_DO_MMIO) {

				/*

				 * Read-modify-write.  Back to userspace.

				 */

				kvm_run->exit_reason = KVM_EXIT_MMIO;

				r = 0;

				goto out;

			}

		}

	}



	vcpu->mmio_needed = 0;



	if (kvm_run->exit_reason == KVM_EXIT_HYPERCALL) {

		kvm_arch_ops->cache_regs(vcpu);