Revert "x86/efi: Build our own page table structures"

BugLink: http://bugs.launchpad.net/bugs/1745047

This reverts commit 36e0f05a which is
commit 67a9108e upstream.

Turns there was too many other issues with this patch to make it viable
for the stable tree.
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: linux-efi@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "Ghannam, Yazen" <Yazen.Ghannam@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/include/asm/efi.h

@@ -136,7 +136,6 @@ extern void __init efi_memory_uc(u64 addr, unsigned long size);
 extern void __init efi_map_region(efi_memory_desc_t *md);
 extern void __init efi_map_region_fixed(efi_memory_desc_t *md);
 extern void efi_sync_low_kernel_mappings(void);
-extern int __init efi_alloc_page_tables(void);
 extern int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages);
 extern void __init efi_cleanup_page_tables(unsigned long pa_memmap, unsigned num_pages);
 extern void __init old_map_region(efi_memory_desc_t *md);

arch/x86/platform/efi/efi.c

@@ -869,7 +869,7 @@ static void __init kexec_enter_virtual_mode(void)
  * This function will switch the EFI runtime services to virtual mode.
  * Essentially, we look through the EFI memmap and map every region that
  * has the runtime attribute bit set in its memory descriptor into the
- * efi_pgd page table.
+ * ->trampoline_pgd page table using a top-down VA allocation scheme.
  *
  * The old method which used to update that memory descriptor with the
  * virtual address obtained from ioremap() is still supported when the
@@ -879,8 +879,8 @@ static void __init kexec_enter_virtual_mode(void)
  *
  * The new method does a pagetable switch in a preemption-safe manner
  * so that we're in a different address space when calling a runtime
- * function. For function arguments passing we do copy the PUDs of the
- * kernel page table into efi_pgd prior to each call.
+ * function. For function arguments passing we do copy the PGDs of the
+ * kernel page table into ->trampoline_pgd prior to each call.
  *
  * Specially for kexec boot, efi runtime maps in previous kernel should
  * be passed in via setup_data. In that case runtime ranges will be mapped
@@ -895,12 +895,6 @@ static void __init __efi_enter_virtual_mode(void)
 
 	efi.systab = NULL;
 
-	if (efi_alloc_page_tables()) {
-		pr_err("Failed to allocate EFI page tables\n");
-		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
-		return;
-	}
-
 	efi_merge_regions();
 	new_memmap = efi_map_regions(&count, &pg_shift);
 	if (!new_memmap) {
@@ -960,11 +954,28 @@ static void __init __efi_enter_virtual_mode(void)
 	efi_runtime_mkexec();
 
 	/*
-	 * We mapped the descriptor array into the EFI pagetable above
-	 * but we're not unmapping it here because if we're running in
-	 * EFI mixed mode we need all of memory to be accessible when
-	 * we pass parameters to the EFI runtime services in the
-	 * thunking code.
+	 * We mapped the descriptor array into the EFI pagetable above but we're
+	 * not unmapping it here. Here's why:
+	 *
+	 * We're copying select PGDs from the kernel page table to the EFI page
+	 * table and when we do so and make changes to those PGDs like unmapping
+	 * stuff from them, those changes appear in the kernel page table and we
+	 * go boom.
+	 *
+	 * From setup_real_mode():
+	 *
+	 * ...
+	 * trampoline_pgd[0] = init_level4_pgt[pgd_index(__PAGE_OFFSET)].pgd;
+	 *
+	 * In this particular case, our allocation is in PGD 0 of the EFI page
+	 * table but we've copied that PGD from PGD[272] of the EFI page table:
+	 *
+	 *	pgd_index(__PAGE_OFFSET = 0xffff880000000000) = 272
+	 *
+	 * where the direct memory mapping in kernel space is.
+	 *
+	 * new_memmap's VA comes from that direct mapping and thus clearing it,
+	 * it would get cleared in the kernel page table too.
 	 *
 	 * efi_cleanup_page_tables(__pa(new_memmap), 1 << pg_shift);
 	 */

arch/x86/platform/efi/efi_32.c

@@ -38,11 +38,6 @@
  * say 0 - 3G.
  */
 
-int __init efi_alloc_page_tables(void)
-{
-	return 0;
-}
-
 void efi_sync_low_kernel_mappings(void) {}
 void __init efi_dump_pagetable(void) {}
 int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)

arch/x86/platform/efi/efi_64.c

@@ -40,7 +40,6 @@
 #include <asm/fixmap.h>
 #include <asm/realmode.h>
 #include <asm/time.h>
-#include <asm/pgalloc.h>
 
 /*
  * We allocate runtime services regions bottom-up, starting from -4G, i.e.
@@ -122,92 +121,22 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	early_code_mapping_set_exec(0);
 }
 
-static pgd_t *efi_pgd;
-
-/*
- * We need our own copy of the higher levels of the page tables
- * because we want to avoid inserting EFI region mappings (EFI_VA_END
- * to EFI_VA_START) into the standard kernel page tables. Everything
- * else can be shared, see efi_sync_low_kernel_mappings().
- */
-int __init efi_alloc_page_tables(void)
-{
-	pgd_t *pgd;
-	pud_t *pud;
-	gfp_t gfp_mask;
-
-	if (efi_enabled(EFI_OLD_MEMMAP))
-		return 0;
-
-	gfp_mask = GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO;
-	efi_pgd = (pgd_t *)__get_free_page(gfp_mask);
-	if (!efi_pgd)
-		return -ENOMEM;
-
-	pgd = efi_pgd + pgd_index(EFI_VA_END);
-
-	pud = pud_alloc_one(NULL, 0);
-	if (!pud) {
-		free_page((unsigned long)efi_pgd);
-		return -ENOMEM;
-	}
-
-	pgd_populate(NULL, pgd, pud);
-
-	return 0;
-}
-
 /*
  * Add low kernel mappings for passing arguments to EFI functions.
  */
 void efi_sync_low_kernel_mappings(void)
 {
-	unsigned num_entries;
-	pgd_t *pgd_k, *pgd_efi;
-	pud_t *pud_k, *pud_efi;
+	unsigned num_pgds;
+	pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
 
 	if (efi_enabled(EFI_OLD_MEMMAP))
 		return;
 
-	/*
-	 * We can share all PGD entries apart from the one entry that
-	 * covers the EFI runtime mapping space.
-	 *
-	 * Make sure the EFI runtime region mappings are guaranteed to
-	 * only span a single PGD entry and that the entry also maps
-	 * other important kernel regions.
-	 */
-	BUILD_BUG_ON(pgd_index(EFI_VA_END) != pgd_index(MODULES_END));
-	BUILD_BUG_ON((EFI_VA_START & PGDIR_MASK) !=
-			(EFI_VA_END & PGDIR_MASK));
-
-	pgd_efi = efi_pgd + pgd_index(PAGE_OFFSET);
-	pgd_k = pgd_offset_k(PAGE_OFFSET);
-
-	num_entries = pgd_index(EFI_VA_END) - pgd_index(PAGE_OFFSET);
-	memcpy(pgd_efi, pgd_k, sizeof(pgd_t) * num_entries);
+	num_pgds = pgd_index(MODULES_END - 1) - pgd_index(PAGE_OFFSET);
 
-	/*
-	 * We share all the PUD entries apart from those that map the
-	 * EFI regions. Copy around them.
-	 */
-	BUILD_BUG_ON((EFI_VA_START & ~PUD_MASK) != 0);
-	BUILD_BUG_ON((EFI_VA_END & ~PUD_MASK) != 0);
-
-	pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
-	pud_efi = pud_offset(pgd_efi, 0);
-
-	pgd_k = pgd_offset_k(EFI_VA_END);
-	pud_k = pud_offset(pgd_k, 0);
-
-	num_entries = pud_index(EFI_VA_END);
-	memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);
-
-	pud_efi = pud_offset(pgd_efi, EFI_VA_START);
-	pud_k = pud_offset(pgd_k, EFI_VA_START);
-
-	num_entries = PTRS_PER_PUD - pud_index(EFI_VA_START);
-	memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);
+	memcpy(pgd + pgd_index(PAGE_OFFSET),
+		init_mm.pgd + pgd_index(PAGE_OFFSET),
+		sizeof(pgd_t) * num_pgds);
 }
 
 int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
@@ -220,8 +149,8 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	if (efi_enabled(EFI_OLD_MEMMAP))
 		return 0;
 
-	efi_scratch.efi_pgt = (pgd_t *)__pa(efi_pgd);
-	pgd = efi_pgd;
+	efi_scratch.efi_pgt = (pgd_t *)(unsigned long)real_mode_header->trampoline_pgd;
+	pgd = __va(efi_scratch.efi_pgt);
 
 	/*
 	 * It can happen that the physical address of new_memmap lands in memory
@@ -267,14 +196,16 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 
 void __init efi_cleanup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 {
-	kernel_unmap_pages_in_pgd(efi_pgd, pa_memmap, num_pages);
+	pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
+
+	kernel_unmap_pages_in_pgd(pgd, pa_memmap, num_pages);
 }
 
 static void __init __map_region(efi_memory_desc_t *md, u64 va)
 {
+	pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
 	unsigned long flags = 0;
 	unsigned long pfn;
-	pgd_t *pgd = efi_pgd;
 
 	if (!(md->attribute & EFI_MEMORY_WB))
 		flags |= _PAGE_PCD;
@@ -383,7 +314,9 @@ void __init efi_runtime_mkexec(void)
 void __init efi_dump_pagetable(void)
 {
 #ifdef CONFIG_EFI_PGT_DUMP
-	ptdump_walk_pgd_level(NULL, efi_pgd);
+	pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
+
+	ptdump_walk_pgd_level(NULL, pgd);
 #endif
 }