arm/arm64: KVM: avoid unnecessary guest register mangling on MMIO read

Currently we mangle the endianness of the guest's register even on an
MMIO _read_, where it is completely useless, because we will not use
the value of that register.
Rework the io_mem_abort() function to clearly separate between reads
and writes and only do the endianness mangling on MMIO writes.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
index 4cb5a93..5d3bfc0 100644 (file)
--- a/arch/arm/kvm/mmio.c
+++ b/arch/arm/kvm/mmio.c
@@ -187,15 +187,18 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
        }
 
        rt = vcpu->arch.mmio_decode.rt;
-       data = vcpu_data_guest_to_host(vcpu, *vcpu_reg(vcpu, rt), mmio.len);
 
-       trace_kvm_mmio((mmio.is_write) ? KVM_TRACE_MMIO_WRITE :
-                                        KVM_TRACE_MMIO_READ_UNSATISFIED,
-                       mmio.len, fault_ipa,
-                       (mmio.is_write) ? data : 0);
+       if (mmio.is_write) {
+               data = vcpu_data_guest_to_host(vcpu, *vcpu_reg(vcpu, rt),
+                                              mmio.len);
 
-       if (mmio.is_write)
+               trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, mmio.len,
+                              fault_ipa, data);
                mmio_write_buf(mmio.data, mmio.len, data);
+       } else {
+               trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, mmio.len,
+                              fault_ipa, 0);
+       }
 
        if (vgic_handle_mmio(vcpu, run, &mmio))
                return 1;