Commit 35ab3b77 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: drop PIO from unregistered devices 



KVM protects the device list with SRCU, and therefore different calls
to kvm_io_bus_read()/kvm_io_bus_write() can very well see different
incarnations of kvm->buses.  If userspace unregisters a device while
vCPUs are running there is no well-defined result.  This patch applies
a safe fallback by returning early from emulator_pio_in_out().  This
corresponds to returning zeroes from IN, and dropping the writes on
the floor for OUT.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0f87ac23

arch/x86/kvm/x86.c

+13 −3
Original line number Diff line number Diff line
@@ -7593,8 +7593,19 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size, 
			r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, port, size, data);

		else

			r = kvm_io_bus_write(vcpu, KVM_PIO_BUS, port, size, data);

		if (r)



		if (r) {

			if (i == 0)

				goto userspace_io;



			/*

			 * Userspace must have unregistered the device while PIO

			 * was running.  Drop writes / read as 0 (the buffer

			 * was zeroed in __emulator_pio_in).

			 */

			break;

		}



		data += size;

	}

	return 1;
@@ -7606,7 +7617,6 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size, 
	vcpu->run->io.data_offset = KVM_PIO_PAGE_OFFSET * PAGE_SIZE;

	vcpu->run->io.count = count;

	vcpu->run->io.port = port;



	return 0;

}