arm64: KVM: Do not corrupt registers on failed 64bit CP read

If we fail to emulate a mrrc instruction, we:
1) deliver an exception,
2) spit a nastygram on the console,
3) write back some garbage to Rt/Rt2

While 1) and 2) are perfectly acceptable, 3) is out of the scope of
the architecture... Let's mimick the code in kvm_handle_cp_32 and
be more cautious.

Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 2f4418e..582d68e 100644 (file)
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1678,20 +1678,25 @@ static int kvm_handle_cp_64(struct kvm_vcpu *vcpu,
                params.regval |= vcpu_get_reg(vcpu, Rt2) << 32;
        }
 
-       if (!emulate_cp(vcpu, &params, target_specific, nr_specific))
-               goto out;
-       if (!emulate_cp(vcpu, &params, global, nr_global))
-               goto out;
-
-       unhandled_cp_access(vcpu, &params);
+       /*
+        * Try to emulate the coprocessor access using the target
+        * specific table first, and using the global table afterwards.
+        * If either of the tables contains a handler, handle the
+        * potential register operation in the case of a read and return
+        * with success.
+        */
+       if (!emulate_cp(vcpu, &params, target_specific, nr_specific) ||
+           !emulate_cp(vcpu, &params, global, nr_global)) {
+               /* Split up the value between registers for the read side */
+               if (!params.is_write) {
+                       vcpu_set_reg(vcpu, Rt, lower_32_bits(params.regval));
+                       vcpu_set_reg(vcpu, Rt2, upper_32_bits(params.regval));
+               }
 
-out:
-       /* Split up the value between registers for the read side */
-       if (!params.is_write) {
-               vcpu_set_reg(vcpu, Rt, lower_32_bits(params.regval));
-               vcpu_set_reg(vcpu, Rt2, upper_32_bits(params.regval));
+               return 1;
        }
 
+       unhandled_cp_access(vcpu, &params);
        return 1;
 }