Commit 2113c5f6 authored Aug 22, 2019 by Andrew Jones Committed by Marc Zyngier Aug 22, 2019

KVM: arm/arm64: Only skip MMIO insn once



If after an MMIO exit to userspace a VCPU is immediately run with an
immediate_exit request, such as when a signal is delivered or an MMIO
emulation completion is needed, then the VCPU completes the MMIO
emulation and immediately returns to userspace. As the exit_reason
does not get changed from KVM_EXIT_MMIO in these cases we have to
be careful not to complete the MMIO emulation again, when the VCPU is
eventually run again, because the emulation does an instruction skip
(and doing too many skips would be a waste of guest code :-) We need
to use additional VCPU state to track if the emulation is complete.
As luck would have it, we already have 'mmio_needed', which even
appears to be used in this way by other architectures already.

Fixes: 0d640732 ("arm64: KVM: Skip MMIO insn after emulation")
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

parent 16e604a4

virt/kvm/arm/mmio.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu vcpu, struct kvm_run run)
		unsigned int len;
		int mask;

		/* Detect an already handled MMIO return */
		if (unlikely(!vcpu->mmio_needed))
		return 0;

		vcpu->mmio_needed = 0;

		if (!run->mmio.is_write) {
		len = run->mmio.len;
		if (len > sizeof(unsigned long))
		@@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu vcpu, struct kvm_run run,
		run->mmio.is_write = is_write;
		run->mmio.phys_addr = fault_ipa;
		run->mmio.len = len;
		vcpu->mmio_needed = 1;

		if (!ret) {
		/* We handled the access successfully in the kernel. */

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