arm64: KVM: Skip MMIO insn after emulation

When we emulate an MMIO instruction, we advance the CPU state within
decode_hsr(), before emulating the instruction effects.

Having this logic in decode_hsr() is opaque, and advancing the state
before emulation is problematic. It gets in the way of applying
consistent single-step logic, and it prevents us from being able to fail
an MMIO instruction with a synchronous exception.

Clean this up by only advancing the CPU state *after* the effects of the
instruction are emulated.

Cc: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index dac7ceb1a677..08443a15e6be 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -117,6 +117,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
                 vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data);
         }
 
+        /*
+         * The MMIO instruction is emulated and should not be re-executed
+         * in the guest.
+         */
+        kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
+
         return 0;
 }
 
@@ -144,11 +150,6 @@ static int decode_hsr(struct kvm_vcpu *vcpu, bool *is_write, int *len)
         vcpu->arch.mmio_decode.sign_extend = sign_extend;
         vcpu->arch.mmio_decode.rt = rt;
 
-        /*
-         * The MMIO instruction is emulated and should not be re-executed
-         * in the guest.
-         */
-        kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
         return 0;
 }