Commit eaed8955 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

x86/efi/mixed: Check CPU compatibility without relying on verify_cpu() 



In order for the EFI mixed mode startup code to be reusable in a context
where the legacy decompressor is not used, replace the call to
verify_cpu() [which performs an elaborate set of checks] with a simple
check against the 'long mode' bit in the appropriate CPUID leaf.

This is reasonable, given that EFI support is implied when booting in
this manner, and so there is no need to consider very old CPUs when
performing this check.

Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent dac628e9

arch/x86/boot/compressed/efi_mixed.S

+9 −13
Original line number Diff line number Diff line
@@ -279,24 +279,20 @@ SYM_FUNC_END(efi32_entry) 
 *			       efi_system_table_32_t *sys_table)

 */

SYM_FUNC_START(efi32_pe_entry)

	pushl	%ebp

	movl	%esp, %ebp

	pushl	%ebx				// save callee-save registers

	pushl	%edi



	call	verify_cpu			// check for long mode support

	testl	%eax, %eax

	movl	$0x80000003, %eax		// EFI_UNSUPPORTED

	jnz	2f



	movl	8(%ebp), %ecx			// image_handle

	movl	12(%ebp), %edx			// sys_table

	/* Check whether the CPU supports long mode */

	movl	$0x80000001, %eax		// assume extended info support

	cpuid

	btl	$29, %edx			// check long mode bit

	jnc	1f

	leal	8(%esp), %esp			// preserve stack alignment

	movl	(%esp), %ecx			// image_handle

	movl	4(%esp), %edx			// sys_table

	jmp	efi32_entry			// pass %ecx, %edx

						// no other registers remain live



2:	popl	%edi				// restore callee-save registers

1:	movl	$0x80000003, %eax		// EFI_UNSUPPORTED

	popl	%ebx

	leave

	RET

SYM_FUNC_END(efi32_pe_entry)