x86/efi: Add early thunk code to go from 64-bit to 32-bit

Implement the transition code to go from IA32e mode to protected mode in
the EFI boot stub. This is required to use 32-bit EFI services from a
64-bit kernel.

Since EFI boot stub is executed in an identity-mapped region, there's
not much we need to do before invoking the 32-bit EFI boot services.
However, we do reload the firmware's global descriptor table
(efi32_boot_gdt) in case things like timer events are still running in
the firmware.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

diff --git a/arch/x86/boot/compressed/efi_stub_64.S b/arch/x86/boot/compressed/efi_stub_64.S
index cedc60de86eb71eb8d51f495f1f9d9b799efedf1..7ff3632806b18ec9a48bd0ae88bdc7a9e9dbe091 100644 (file)
--- a/arch/x86/boot/compressed/efi_stub_64.S
+++ b/arch/x86/boot/compressed/efi_stub_64.S
@@ -1 +1,30 @@
+#include <asm/segment.h>
+#include <asm/msr.h>
+#include <asm/processor-flags.h>
+
 #include "../../platform/efi/efi_stub_64.S"
+
+#ifdef CONFIG_EFI_MIXED
+       .code64
+       .text
+ENTRY(efi64_thunk)
+       push    %rbp
+       push    %rbx
+
+       subq    $16, %rsp
+       leaq    efi_exit32(%rip), %rax
+       movl    %eax, 8(%rsp)
+       leaq    efi_gdt64(%rip), %rax
+       movl    %eax, 4(%rsp)
+       movl    %eax, 2(%rax)           /* Fixup the gdt base address */
+       leaq    efi32_boot_gdt(%rip), %rax
+       movl    %eax, (%rsp)
+
+       call    __efi64_thunk
+
+       addq    $16, %rsp
+       pop     %rbx
+       pop     %rbp
+       ret
+ENDPROC(efi64_thunk)
+#endif /* CONFIG_EFI_MIXED */

diff --git a/arch/x86/platform/efi/efi_stub_64.S b/arch/x86/platform/efi/efi_stub_64.S
index 88073b1402988b49eb6c5e95f9f801a14d40f144..a790d69cc85e7491db051e79aefb8678739f9f94 100644 (file)
--- a/arch/x86/platform/efi/efi_stub_64.S
+++ b/arch/x86/platform/efi/efi_stub_64.S
@@ -7,6 +7,10 @@
  */
 
 #include <linux/linkage.h>
+#include <asm/segment.h>
+#include <asm/msr.h>
+#include <asm/processor-flags.h>
+#include <asm/page_types.h>
 
 #define SAVE_XMM                       \
        mov %rsp, %rax;                 \
@@ -164,6 +168,152 @@ ENTRY(efi_call6)
        ret
 ENDPROC(efi_call6)
 
+#ifdef CONFIG_EFI_MIXED
+
+/*
+ * We run this function from the 1:1 mapping.
+ *
+ * This function must be invoked with a 1:1 mapped stack.
+ */
+ENTRY(__efi64_thunk)
+       subq    $32, %rsp
+       movl    %esi, 0x0(%rsp)
+       movl    %edx, 0x4(%rsp)
+       movl    %ecx, 0x8(%rsp)
+       movq    %r8, %rsi
+       movl    %esi, 0xc(%rsp)
+       movq    %r9, %rsi
+       movl    %esi,  0x10(%rsp)
+
+       sgdt    save_gdt(%rip)
+
+       leaq    1f(%rip), %rbx
+       movq    %rbx, func_rt_ptr(%rip)
+
+       /* Switch to gdt with 32-bit segments */
+       movl    40(%rsp), %eax
+       lgdt    (%rax)
+
+       leaq    efi_enter32(%rip), %rax
+       pushq   $__KERNEL_CS
+       pushq   %rax
+       lretq
+
+1:     addq    $32, %rsp
+
+       lgdt    save_gdt(%rip)
+
+       /*
+        * Convert 32-bit status code into 64-bit.
+        */
+       test    %rax, %rax
+       jz      1f
+       movl    %eax, %ecx
+       andl    $0x0fffffff, %ecx
+       andl    $0xf0000000, %eax
+       shl     $32, %rax
+       or      %rcx, %rax
+1:
+       ret
+ENDPROC(__efi64_thunk)
+
+ENTRY(efi_exit32)
+       xorq    %rax, %rax
+       movl    %eax, %ds
+       movl    %eax, %es
+       movl    %eax, %ss
+
+       movq    func_rt_ptr(%rip), %rax
+       push    %rax
+       mov     %rdi, %rax
+       ret
+ENDPROC(efi_exit32)
+
+       .code32
+/*
+ * EFI service pointer must be in %edi.
+ *
+ * The stack should represent the 32-bit calling convention.
+ */
+ENTRY(efi_enter32)
+       movl    $__KERNEL_DS, %eax
+       movl    %eax, %ds
+       movl    %eax, %es
+       movl    %eax, %ss
+
+       /* Reload pgtables */
+       movl    %cr3, %eax
+       movl    %eax, %cr3
+
+       /* Disable paging */
+       movl    %cr0, %eax
+       btrl    $X86_CR0_PG_BIT, %eax
+       movl    %eax, %cr0
+
+       /* Disable long mode via EFER */
+       movl    $MSR_EFER, %ecx
+       rdmsr
+       btrl    $_EFER_LME, %eax
+       wrmsr
+
+       call    *%edi
+
+       /* We must preserve return value */
+       movl    %eax, %edi
+
+       movl    44(%esp), %eax
+       movl    %eax, 2(%eax)
+       lgdtl   (%eax)
+
+       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
+
+       movl    48(%esp), %eax
+       pushl   $__KERNEL_CS
+       pushl   %eax
+
+       /* Enable paging */
+       movl    %cr0, %eax
+       btsl    $X86_CR0_PG_BIT, %eax
+       movl    %eax, %cr0
+       lret
+ENDPROC(efi_enter32)
+
+       .data
+       .balign 8
+       .global efi32_boot_gdt
+efi32_boot_gdt:        .word   0
+               .quad   0
+
+save_gdt:      .word   0
+               .quad   0
+func_rt_ptr:   .quad   0
+
+       .global efi_gdt64
+efi_gdt64:
+       .word   efi_gdt64_end - efi_gdt64
+       .long   0                       /* Filled out by user */
+       .word   0
+       .quad   0x0000000000000000      /* NULL descriptor */
+       .quad   0x00af9a000000ffff      /* __KERNEL_CS */
+       .quad   0x00cf92000000ffff      /* __KERNEL_DS */
+       .quad   0x0080890000000000      /* TS descriptor */
+       .quad   0x0000000000000000      /* TS continued */
+efi_gdt64_end:
+#endif /* CONFIG_EFI_MIXED */
+
        .data
 ENTRY(efi_scratch)
        .fill 3,8,0