x86/boot/compressed/64: Detect and handle 5-level paging at boot-time

[linux.git] / arch / x86 / boot / compressed / head_64.S

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 20919b4f31330fbc36528e47cf7dd010e516c31c..fc313e29fe2c4be637ff7d41bfafdc7a29144ba4 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -305,10 +305,18 @@ ENTRY(startup_64)
        leaq    boot_stack_end(%rbx), %rsp
 
 #ifdef CONFIG_X86_5LEVEL
-       /* Check if 5-level paging has already enabled */
-       movq    %cr4, %rax
-       testl   $X86_CR4_LA57, %eax
-       jnz     lvl5
+       /*
+        * Check if we need to enable 5-level paging.
+        * RSI holds real mode data and need to be preserved across
+        * a function call.
+        */
+       pushq   %rsi
+       call    l5_paging_required
+       popq    %rsi
+
+       /* If l5_paging_required() returned zero, we're done here. */
+       cmpq    $0, %rax
+       je      lvl5
 
        /*
         * At this point we are in long mode with 4-level paging enabled,