KVM: arm64: Stop clobbering x0 for HVC_SOFT_RESTART

HVC_SOFT_RESTART is given values for x0-2 that it should installed
before exiting to the new address so should not set x0 to stub HVC
success or failure code.

Fixes: af42f20480bf1 ("arm64: hyp-stub: Zero x0 on successful stub handling")
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200706095259.1338221-1-ascull@google.com

diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index 6e6ed55..e76c0e8 100644 (file)
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -136,11 +136,15 @@ SYM_CODE_START(__kvm_handle_stub_hvc)
 
 1:     cmp     x0, #HVC_RESET_VECTORS
        b.ne    1f
-reset:
+
        /*
-        * Reset kvm back to the hyp stub. Do not clobber x0-x4 in
-        * case we coming via HVC_SOFT_RESTART.
+        * Set the HVC_RESET_VECTORS return code before entering the common
+        * path so that we do not clobber x0-x2 in case we are coming via
+        * HVC_SOFT_RESTART.
         */
+       mov     x0, xzr
+reset:
+       /* Reset kvm back to the hyp stub. */
        mrs     x5, sctlr_el2
        mov_q   x6, SCTLR_ELx_FLAGS
        bic     x5, x5, x6              // Clear SCTL_M and etc
@@ -151,7 +155,6 @@ reset:
        /* Install stub vectors */
        adr_l   x5, __hyp_stub_vectors
        msr     vbar_el2, x5
-       mov     x0, xzr
        eret
 
 1:     /* Bad stub call */