KVM: SVM: adjust register allocation for __svm_vcpu_run()

32-bit ABI uses RAX/RCX/RDX as its argument registers, so they are in
the way of instructions that hardcode their operands such as RDMSR/WRMSR
or VMLOAD/VMRUN/VMSAVE.

In preparation for moving vmload/vmsave to __svm_vcpu_run(), keep
the pointer to the struct vcpu_svm in %rdi.  In particular, it is now
possible to load svm->vmcb01.pa in %rax without clobbering the struct
vcpu_svm pointer.

No functional change intended.

Cc: stable@vger.kernel.org
Fixes: a149180f ("x86: Add magic AMD return-thunk")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/vmenter.S

@@ -54,29 +54,29 @@ SYM_FUNC_START(__svm_vcpu_run)
 	/* Save @vmcb. */
 	push %_ASM_ARG1
 
-	/* Move @svm to RAX. */
-	mov %_ASM_ARG2, %_ASM_AX
+	/* Move @svm to RDI. */
+	mov %_ASM_ARG2, %_ASM_DI
+
+	/* "POP" @vmcb to RAX. */
+	pop %_ASM_AX
 
 	/* Load guest registers. */
-	mov VCPU_RCX(%_ASM_AX), %_ASM_CX
-	mov VCPU_RDX(%_ASM_AX), %_ASM_DX
-	mov VCPU_RBX(%_ASM_AX), %_ASM_BX
-	mov VCPU_RBP(%_ASM_AX), %_ASM_BP
-	mov VCPU_RSI(%_ASM_AX), %_ASM_SI
-	mov VCPU_RDI(%_ASM_AX), %_ASM_DI
+	mov VCPU_RCX(%_ASM_DI), %_ASM_CX
+	mov VCPU_RDX(%_ASM_DI), %_ASM_DX
+	mov VCPU_RBX(%_ASM_DI), %_ASM_BX
+	mov VCPU_RBP(%_ASM_DI), %_ASM_BP
+	mov VCPU_RSI(%_ASM_DI), %_ASM_SI
 #ifdef CONFIG_X86_64
-	mov VCPU_R8 (%_ASM_AX),  %r8
-	mov VCPU_R9 (%_ASM_AX),  %r9
-	mov VCPU_R10(%_ASM_AX), %r10
-	mov VCPU_R11(%_ASM_AX), %r11
-	mov VCPU_R12(%_ASM_AX), %r12
-	mov VCPU_R13(%_ASM_AX), %r13
-	mov VCPU_R14(%_ASM_AX), %r14
-	mov VCPU_R15(%_ASM_AX), %r15
+	mov VCPU_R8 (%_ASM_DI),  %r8
+	mov VCPU_R9 (%_ASM_DI),  %r9
+	mov VCPU_R10(%_ASM_DI), %r10
+	mov VCPU_R11(%_ASM_DI), %r11
+	mov VCPU_R12(%_ASM_DI), %r12
+	mov VCPU_R13(%_ASM_DI), %r13
+	mov VCPU_R14(%_ASM_DI), %r14
+	mov VCPU_R15(%_ASM_DI), %r15
 #endif
-
-	/* "POP" @vmcb to RAX. */
-	pop %_ASM_AX
+	mov VCPU_RDI(%_ASM_DI), %_ASM_DI
 
 	/* Enter guest mode */
 	sti