x86/efi/mixed: Factor out and clean up long mode entry

Entering long mode involves setting the EFER_LME and CR4.PAE bits before
enabling paging by setting CR0.PG bit.

It also involves disabling interrupts, given that the firmware's 32-bit
IDT becomes invalid as soon as the CPU transitions into long mode.

Reloading the CR3 register is not necessary at boot time, given that the
EFI firmware as well as the kernel's EFI stub use a 1:1 mapping of the
32-bit addressable memory in the system.

Break out this code into a separate helper for clarity, and so that it
can be reused in a subsequent patch.

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 b7886e2591fcf15f52d10b56e41cfe081db4dd95..0b6b37b08f82fe2f9ad738e0d844507cafa44063 100644 (file)
--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -170,10 +170,6 @@ SYM_FUNC_START_LOCAL(efi_enter32)
        movl    %edx, %gs
        movl    %edx, %ss
 
-       /* Reload pgtables */
-       movl    %cr3, %eax
-       movl    %eax, %cr3
-
        /* Disable paging */
        movl    %cr0, %eax
        btrl    $X86_CR0_PG_BIT, %eax
@@ -199,30 +195,35 @@ SYM_FUNC_START_LOCAL(efi_enter32)
        lidtl   16(%ebx)
        lgdtl   (%ebx)
 
+       xorl    %eax, %eax
+       lldt    %ax
+
+       call    efi32_enable_long_mode
+
+       pushl   $__KERNEL_CS
+       pushl   %ebp
+       lret
+SYM_FUNC_END(efi_enter32)
+
+SYM_FUNC_START_LOCAL(efi32_enable_long_mode)
        movl    %cr4, %eax
        btsl    $(X86_CR4_PAE_BIT), %eax
        movl    %eax, %cr4
 
-       movl    %cr3, %eax
-       movl    %eax, %cr3
-
        movl    $MSR_EFER, %ecx
        rdmsr
        btsl    $_EFER_LME, %eax
        wrmsr
 
-       xorl    %eax, %eax
-       lldt    %ax
-
-       pushl   $__KERNEL_CS
-       pushl   %ebp
+       /* Disable interrupts - the firmware's IDT does not work in long mode */
+       cli
 
        /* Enable paging */
        movl    %cr0, %eax
        btsl    $X86_CR0_PG_BIT, %eax
        movl    %eax, %cr0
-       lret
-SYM_FUNC_END(efi_enter32)
+       ret
+SYM_FUNC_END(efi32_enable_long_mode)
 
 /*
  * This is the common EFI stub entry point for mixed mode.