KVM: VMX: Invert the ordering of saving guest/host scratch reg at VM-Enter

Switching the ordering allows for an out-of-line path for VM-Fail
that elides saving guest state but still shares the register clearing
with the VM-Exit path.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 996a13e..79b4219 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6382,7 +6382,6 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
        asm(
                /* Store host registers */
                "push %%" _ASM_BP " \n\t"
-               "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */
                "push %%" _ASM_ARG1 " \n\t"
 
                /* Adjust RSP to account for the CALL to vmx_vmenter(). */
@@ -6418,11 +6417,11 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                /* Enter guest mode */
                "call vmx_vmenter\n\t"
 
-               /* Save guest's RCX to the stack placeholder (see above) */
-               "mov %%" _ASM_CX ", %c[wordsize](%%" _ASM_SP ") \n\t"
+               /* Temporarily save guest's RCX. */
+               "push %%" _ASM_CX " \n\t"
 
-               /* Load host's RCX, i.e. the vmx_vcpu pointer */
-               "pop %%" _ASM_CX " \n\t"
+               /* Reload the vcpu_vmx pointer to RCX. */
+               "mov %c[wordsize](%%" _ASM_SP "), %%" _ASM_CX " \n\t"
 
                /* Set vmx->fail based on EFLAGS.{CF,ZF} */
                "setbe %c[fail](%%" _ASM_CX ")\n\t"
@@ -6469,6 +6468,9 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                "xor %%esi, %%esi \n\t"
                "xor %%edi, %%edi \n\t"
                "xor %%ebp, %%ebp \n\t"
+
+               /* "POP" the vcpu_vmx pointer. */
+               "add $%c[wordsize], %%" _ASM_SP " \n\t"
                "pop  %%" _ASM_BP " \n\t"
              : ASM_CALL_CONSTRAINT, "=b"((int){0}),
 #ifdef CONFIG_X86_64