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Subject[PATCH 4.9 153/171] Revert "x86/mm: Expand static page table for fixmap space"
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

This reverts commit 3a8304b7ad2e291777e8499e39390145d932a2fd, which was
upstream commit 05ab1d8a4b36ee912b7087c6da127439ed0a903e.

Ben Hutchings writes:

This backport is incorrect. The part that updated __startup_64() in
arch/x86/kernel/head64.c was dropped, presumably because that function
doesn't exist in 4.9. However that seems to be an essential of the
fix. In 4.9 the startup_64 routine in arch/x86/kernel/head_64.S would
need to be changed instead.

I also found that this introduces new boot-time warnings on some
systems if CONFIG_DEBUG_WX is enabled.

So, unless someone provides fixes for those issues, I think this should
be reverted for the 4.9 branch.

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/fixmap.h | 10 ----------
arch/x86/include/asm/pgtable_64.h | 3 +--
arch/x86/kernel/head_64.S | 16 ++++------------
arch/x86/mm/pgtable.c | 9 ---------
arch/x86/xen/mmu.c | 8 ++------
5 files changed, 7 insertions(+), 39 deletions(-)

--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -14,16 +14,6 @@
#ifndef _ASM_X86_FIXMAP_H
#define _ASM_X86_FIXMAP_H

-/*
- * Exposed to assembly code for setting up initial page tables. Cannot be
- * calculated in assembly code (fixmap entries are an enum), but is sanity
- * checked in the actual fixmap C code to make sure that the fixmap is
- * covered fully.
- */
-#define FIXMAP_PMD_NUM 2
-/* fixmap starts downwards from the 507th entry in level2_fixmap_pgt */
-#define FIXMAP_PMD_TOP 507
-
#ifndef __ASSEMBLY__
#include <linux/kernel.h>
#include <asm/acpi.h>
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -13,14 +13,13 @@
#include <asm/processor.h>
#include <linux/bitops.h>
#include <linux/threads.h>
-#include <asm/fixmap.h>

extern pud_t level3_kernel_pgt[512];
extern pud_t level3_ident_pgt[512];
extern pmd_t level2_kernel_pgt[512];
extern pmd_t level2_fixmap_pgt[512];
extern pmd_t level2_ident_pgt[512];
-extern pte_t level1_fixmap_pgt[512 * FIXMAP_PMD_NUM];
+extern pte_t level1_fixmap_pgt[512];
extern pgd_t init_level4_pgt[];

#define swapper_pg_dir init_level4_pgt
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -23,7 +23,6 @@
#include "../entry/calling.h"
#include <asm/export.h>
#include <asm/nospec-branch.h>
-#include <asm/fixmap.h>

#ifdef CONFIG_PARAVIRT
#include <asm/asm-offsets.h>
@@ -494,20 +493,13 @@ NEXT_PAGE(level2_kernel_pgt)
KERNEL_IMAGE_SIZE/PMD_SIZE)

NEXT_PAGE(level2_fixmap_pgt)
- .fill (512 - 4 - FIXMAP_PMD_NUM),8,0
- pgtno = 0
- .rept (FIXMAP_PMD_NUM)
- .quad level1_fixmap_pgt + (pgtno << PAGE_SHIFT) - __START_KERNEL_map \
- + _PAGE_TABLE;
- pgtno = pgtno + 1
- .endr
- /* 6 MB reserved space + a 2MB hole */
- .fill 4,8,0
+ .fill 506,8,0
+ .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+ /* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
+ .fill 5,8,0

NEXT_PAGE(level1_fixmap_pgt)
- .rept (FIXMAP_PMD_NUM)
.fill 512,8,0
- .endr

#undef PMDS

--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -536,15 +536,6 @@ void __native_set_fixmap(enum fixed_addr
{
unsigned long address = __fix_to_virt(idx);

-#ifdef CONFIG_X86_64
- /*
- * Ensure that the static initial page tables are covering the
- * fixmap completely.
- */
- BUILD_BUG_ON(__end_of_permanent_fixed_addresses >
- (FIXMAP_PMD_NUM * PTRS_PER_PTE));
-#endif
-
if (idx >= __end_of_fixed_addresses) {
BUG();
return;
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1936,7 +1936,7 @@ void __init xen_setup_kernel_pagetable(p
* L3_k[511] -> level2_fixmap_pgt */
convert_pfn_mfn(level3_kernel_pgt);

- /* L3_k[511][508-FIXMAP_PMD_NUM ... 507] -> level1_fixmap_pgt */
+ /* L3_k[511][506] -> level1_fixmap_pgt */
convert_pfn_mfn(level2_fixmap_pgt);
}
/* We get [511][511] and have Xen's version of level2_kernel_pgt */
@@ -1970,11 +1970,7 @@ void __init xen_setup_kernel_pagetable(p
set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
-
- for (i = 0; i < FIXMAP_PMD_NUM; i++) {
- set_page_prot(level1_fixmap_pgt + i * PTRS_PER_PTE,
- PAGE_KERNEL_RO);
- }
+ set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO);

/* Pin down new L4 */
pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,

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