KVM: arm64: Don't clobber x4 in __do_hyp_init

arm_smccc_1_1_hvc() only adds write contraints for x0-3 in the inline
assembly for the HVC instruction so make sure those are the only
registers that change when __do_hyp_init is called.

Tested-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210125145415.122439-3-ascull@google.com

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index 31b060a..b17bf19 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -47,6 +47,8 @@ __invalid:
        b       .
 
        /*
+        * Only uses x0..x3 so as to not clobber callee-saved SMCCC registers.
+        *
         * x0: SMCCC function ID
         * x1: struct kvm_nvhe_init_params PA
         */
@@ -70,9 +72,9 @@ __do_hyp_init:
        eret
 
 1:     mov     x0, x1
-       mov     x4, lr
-       bl      ___kvm_hyp_init
-       mov     lr, x4
+       mov     x3, lr
+       bl      ___kvm_hyp_init                 // Clobbers x0..x2
+       mov     lr, x3
 
        /* Hello, World! */
        mov     x0, #SMCCC_RET_SUCCESS
@@ -82,8 +84,8 @@ SYM_CODE_END(__kvm_hyp_init)
 /*
  * Initialize the hypervisor in EL2.
  *
- * Only uses x0..x3 so as to not clobber callee-saved SMCCC registers
- * and leave x4 for the caller.
+ * Only uses x0..x2 so as to not clobber callee-saved SMCCC registers
+ * and leave x3 for the caller.
  *
  * x0: struct kvm_nvhe_init_params PA
  */
@@ -112,9 +114,9 @@ alternative_else_nop_endif
        /*
         * Set the PS bits in TCR_EL2.
         */
-       ldr     x1, [x0, #NVHE_INIT_TCR_EL2]
-       tcr_compute_pa_size x1, #TCR_EL2_PS_SHIFT, x2, x3
-       msr     tcr_el2, x1
+       ldr     x0, [x0, #NVHE_INIT_TCR_EL2]
+       tcr_compute_pa_size x0, #TCR_EL2_PS_SHIFT, x1, x2
+       msr     tcr_el2, x0
 
        isb
 
@@ -193,7 +195,7 @@ SYM_CODE_START_LOCAL(__kvm_hyp_init_cpu)
 
        /* Enable MMU, set vectors and stack. */
        mov     x0, x28
-       bl      ___kvm_hyp_init                 // Clobbers x0..x3
+       bl      ___kvm_hyp_init                 // Clobbers x0..x2
 
        /* Leave idmap. */
        mov     x0, x29