x86/efi: Dump the EFI page table

This is very useful for debugging issues with the recently added
pagetable switching code for EFI virtual mode.

Signed-off-by: Borislav Petkov <[e-mail]>
Tested-by: Toshi Kani <[e-mail]>
Signed-off-by: Matt Fleming <[e-mail]>

arch/x86/Kconfig.debug

···
 	  kernel.
 	  If in doubt, say "N"
 
+config EFI_PGT_DUMP
+	bool "Dump the EFI pagetable"
+	depends on EFI && X86_PTDUMP
+	---help---
+	  Enable this if you want to dump the EFI page table before
+	  enabling virtual mode. This can be used to debug miscellaneous
+	  issues with the mapping of the EFI runtime regions into that
+	  table.
+
 config DEBUG_RODATA
 	bool "Write protect kernel read-only data structures"
 	default y

arch/x86/include/asm/efi.h

···
 extern void __init old_map_region(efi_memory_desc_t *md);
 extern void __init runtime_code_page_mkexec(void);
 extern void __init efi_runtime_mkexec(void);
+extern void __init efi_dump_pagetable(void);
 
 struct efi_setup_data {
 	u64 fw_vendor;

arch/x86/platform/efi/efi.c

···
 
 	efi_setup_page_tables();
 	efi_sync_low_kernel_mappings();
+	efi_dump_pagetable();
 
 	if (!efi_setup) {
 		status = phys_efi_set_virtual_address_map(

arch/x86/platform/efi/efi_32.c

···
 
 void efi_sync_low_kernel_mappings(void) {}
 void efi_setup_page_tables(void) {}
+void __init efi_dump_pagetable(void) {}
 
 void __init efi_map_region(efi_memory_desc_t *md)
 {

arch/x86/platform/efi/efi_64.c

···
 	if (__supported_pte_mask & _PAGE_NX)
 		runtime_code_page_mkexec();
 }
+
+void __init efi_dump_pagetable(void)
+{
+#ifdef CONFIG_EFI_PGT_DUMP
+	pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
+
+	ptdump_walk_pgd_level(NULL, pgd);
+#endif
+}