[PATCH v2 2/2] KVM: VMX: guard regparm(0) on vmread_error_trampoline for x86_32 only

[Clark Williams <clrkwllms@kernel.org>]

[ Upstream commit 0b5e7a16a0a79a3742f0df9e45bca46f01b40e6a ]

regparm(0) overrides the kernel's -mregparm=3 convention on x86-32 so
that vmread_error_trampoline receives its arguments on the stack, matching
the inline asm callers that push args before the call.  On x86-64 the
attribute is a no-op and newer GCC now emits -Wattributes for it, which
becomes a build error under -Werror.  Guard it with CONFIG_X86_32.

[ clrkwllms: the upstream commit redesigns the trampoline declaration as
  an opaque symbol; this simpler approach guards the regparm(0) attribute
  with CONFIG_X86_32 since the attribute is only meaningful on x86-32. ]

Assisted-by: Claude:claude-sonnet-4.6
Signed-off-by: Clark Williams <clrkwllms@kernel.org>
---
 arch/x86/kvm/vmx/vmx_ops.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx_ops.h b/arch/x86/kvm/vmx/vmx_ops.h
index 5edab28dfb2e..50328be40b2b 100644
--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -11,8 +11,11 @@
 #include "../x86.h"
 
 void vmread_error(unsigned long field, bool fault);
-__attribute__((regparm(0))) void vmread_error_trampoline(unsigned long field,
-							 bool fault);
+/* regparm(0) overrides -mregparm=3 so args are stack-passed, matching asm callers */
+#ifdef CONFIG_X86_32
+__attribute__((regparm(0)))
+#endif
+void vmread_error_trampoline(unsigned long field, bool fault);
 void vmwrite_error(unsigned long field, unsigned long value);
 void vmclear_error(struct vmcs *vmcs, u64 phys_addr);
 void vmptrld_error(struct vmcs *vmcs, u64 phys_addr);
-- 
2.54.0