KVM: VMX: Do not declare vmread_error() asmlinkage

There is no need to declare vmread_error() asmlinkage, its arguments
can be passed via registers for both 32-bit and 64-bit targets.
Function argument registers are considered call-clobbered registers,
they are saved in the trampoline just before the function call and
restored afterwards.

Dropping "asmlinkage" patch unifies trampoline function argument handling
between 32-bit and 64-bit targets and improves generated code for 32-bit
targets.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20220817144045.3206-1-ubizjak@gmail.comSigned-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmenter.S

@@ -292,22 +292,13 @@ SYM_FUNC_START(vmread_error_trampoline)
 	push %r10
 	push %r11
 #endif
-#ifdef CONFIG_X86_64
+
 	/* Load @field and @fault to arg1 and arg2 respectively. */
-	mov 3*WORD_SIZE(%rbp), %_ASM_ARG2
-	mov 2*WORD_SIZE(%rbp), %_ASM_ARG1
-#else
-	/* Parameters are passed on the stack for 32-bit (see asmlinkage). */
-	push 3*WORD_SIZE(%ebp)
-	push 2*WORD_SIZE(%ebp)
-#endif
+	mov 3*WORD_SIZE(%_ASM_BP), %_ASM_ARG2
+	mov 2*WORD_SIZE(%_ASM_BP), %_ASM_ARG1
 
 	call vmread_error
 
-#ifndef CONFIG_X86_64
-	add $8, %esp
-#endif
-
 	/* Zero out @fault, which will be popped into the result register. */
 	_ASM_MOV $0, 3*WORD_SIZE(%_ASM_BP)
 

arch/x86/kvm/vmx/vmx.c

@@ -439,7 +439,7 @@ do {					\
 	pr_warn_ratelimited(fmt);	\
 } while (0)
 
-asmlinkage void vmread_error(unsigned long field, bool fault)
+void vmread_error(unsigned long field, bool fault)
 {
 	if (fault)
 		kvm_spurious_fault();

arch/x86/kvm/vmx/vmx_ops.h

@@ -10,7 +10,7 @@
 #include "vmcs.h"
 #include "../x86.h"
 
-asmlinkage void vmread_error(unsigned long field, bool fault);
+void vmread_error(unsigned long field, bool fault);
 __attribute__((regparm(0))) void vmread_error_trampoline(unsigned long field,
 							 bool fault);
 void vmwrite_error(unsigned long field, unsigned long value);