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: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S
index d681e30c6732c81346a2784d31e0219241c8ec1c..b7886e2591fcf15f52d10b56e41cfe081db4dd95 100644 (file)
--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -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)