Re: [PATCH 2/9] arm64: mm: Flip kernel VA space

Bhupesh Sharma <bhsharma@xxxxxxxxxx> · Wed, 3 Apr 2019 17:14:53 +0530

Hi Steve,

On 02/18/2019 10:32 PM, Steve Capper wrote:
Put the direct linear map in the lower addresses of the kernel VA range
and everything else in the higher ranges.

This allows us to make room for an inline KASAN shadow that operates
under both 48 and 52 bit kernel VA sizes. For example with a 52-bit VA,
if KASAN_SHADOW_END < 0xFFF8000000000000 (it is in the lower addresses
of the kernel VA range), this will be below the start of the minimum
48-bit kernel VA address of 0xFFFF000000000000.

We need to adjust:
  *) KASAN shadow region placement logic,
  *) KASAN_SHADOW_OFFSET computation logic,
  *) virt_to_phys, phys_to_virt checks,
  *) page table dumper.

These are all small changes, that need to take place atomically, so they
are bundled into this commit.

May be its a good opportunity to update the memory layout documentation 
(see [0]) with this patch, where we say:

AArch64 Linux memory layout with 64KB pages + 3 levels:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000ffffffffffff	 256TB		user
ffff000000000000	ffffffffffffffff	 256TB		kernel

Now, with 52-bit addressing capabilities the kernel space would start 
from 0xFFF0_0000_0000_0000 and go all the way up to 0xFFFF_FFFF_FFFF_FFFF.

Also the 'Translation table lookup with 64KB pages:' section needs an 
update to indicate increased bits for 52-bit PA changes.

Alternatively we may want to have a doc dedicated to 52-bit address 
space details on arm64, similar to what we have currently for x86 (see 
[1a] and [1b]) where we can capture some of the details already 
available in your excellent talk on this subject (see [2]).

If you need any help with the same, do let me know.

[0]. https://www.kernel.org/doc/Documentation/arm64/memory.txt
[1a]. 
https://github.com/torvalds/linux/blob/master/Documentation/x86/x86_64/5level-paging.txt
[1b]. 
https://github.com/torvalds/linux/blob/master/Documentation/x86/x86_64/mm.txt
[2]. https://connect.linaro.org/resources/yvr18/sessions/yvr18-119/

Thanks,
Bhupesh

Signed-off-by: Steve Capper <steve.capper@xxxxxxx>
---
  arch/arm64/Makefile              |  2 +-
  arch/arm64/include/asm/memory.h  | 10 +++++-----
  arch/arm64/include/asm/pgtable.h |  2 +-
  arch/arm64/mm/dump.c             |  8 ++++----
  arch/arm64/mm/init.c             |  9 +--------
  arch/arm64/mm/kasan_init.c       |  6 +++---
  arch/arm64/mm/mmu.c              |  4 ++--
  7 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index b025304bde46..2dad2ae6b181 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -115,7 +115,7 @@ KBUILD_AFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
  #				 - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
  # in 32-bit arithmetic
  KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
-	(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
+	(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 1 - 32))) \
  	+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
  	- (1 << (64 - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) )) )
  
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 617071dbad06..46a7aba44e9b 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -49,10 +49,10 @@
   */
  #define VA_BITS			(CONFIG_ARM64_VA_BITS)
  #define VA_START		(UL(0xffffffffffffffff) - \
-	(UL(1) << VA_BITS) + 1)
-#define PAGE_OFFSET		(UL(0xffffffffffffffff) - \
  	(UL(1) << (VA_BITS - 1)) + 1)
-#define PAGE_OFFSET_END		(~0UL)
+#define PAGE_OFFSET		(UL(0xffffffffffffffff) - \
+	(UL(1) << VA_BITS) + 1)
+#define PAGE_OFFSET_END		(VA_START)
  #define KIMAGE_VADDR		(MODULES_END)
  #define BPF_JIT_REGION_START	(VA_START + KASAN_SHADOW_SIZE)
  #define BPF_JIT_REGION_SIZE	(SZ_128M)
@@ -60,7 +60,7 @@
  #define MODULES_END		(MODULES_VADDR + MODULES_VSIZE)
  #define MODULES_VADDR		(BPF_JIT_REGION_END)
  #define MODULES_VSIZE		(SZ_128M)
-#define VMEMMAP_START		(PAGE_OFFSET - VMEMMAP_SIZE)
+#define VMEMMAP_START		(-VMEMMAP_SIZE)
  #define PCI_IO_END		(VMEMMAP_START - SZ_2M)
  #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
  #define FIXADDR_TOP		(PCI_IO_START - SZ_2M)
@@ -243,7 +243,7 @@ extern u64			vabits_user;
   * space. Testing the top bit for the start of the region is a
   * sufficient check.
   */
-#define __is_lm_address(addr)	(!!((addr) & BIT(VA_BITS - 1)))
+#define __is_lm_address(addr)	(!((addr) & BIT(VA_BITS - 1)))
  
  #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
  #define __kimg_to_phys(addr)	((addr) - kimage_voffset)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index de70c1eabf33..766def2ed788 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -32,7 +32,7 @@
   *	and fixed mappings
   */
  #define VMALLOC_START		(MODULES_END)
-#define VMALLOC_END		(PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
+#define VMALLOC_END		(- PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
  
  #define vmemmap			((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
  
diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
index 99bb8facb5cb..3dd9b884bd39 100644
--- a/arch/arm64/mm/dump.c
+++ b/arch/arm64/mm/dump.c
@@ -30,6 +30,8 @@
  #include <asm/ptdump.h>
  
  static const struct addr_marker address_markers[] = {
+	{ PAGE_OFFSET,			"Linear Mapping start" },
+	{ VA_START,			"Linear Mapping end" },
  #ifdef CONFIG_KASAN
  	{ KASAN_SHADOW_START,		"Kasan shadow start" },
  	{ KASAN_SHADOW_END,		"Kasan shadow end" },
@@ -43,10 +45,8 @@ static const struct addr_marker address_markers[] = {
  	{ PCI_IO_START,			"PCI I/O start" },
  	{ PCI_IO_END,			"PCI I/O end" },
  #ifdef CONFIG_SPARSEMEM_VMEMMAP
-	{ VMEMMAP_START,		"vmemmap start" },
-	{ VMEMMAP_START + VMEMMAP_SIZE,	"vmemmap end" },
+	{ VMEMMAP_START,		"vmemmap" },
  #endif
-	{ PAGE_OFFSET,			"Linear mapping" },
  	{ -1,				NULL },
  };
  
@@ -380,7 +380,7 @@ static void ptdump_initialize(void)
  static struct ptdump_info kernel_ptdump_info = {
  	.mm		= &init_mm,
  	.markers	= address_markers,
-	.base_addr	= VA_START,
+	.base_addr	= PAGE_OFFSET,
  };
  
  void ptdump_check_wx(void)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 7205a9085b4d..0574e17fd28d 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -354,7 +354,7 @@ static void __init fdt_enforce_memory_region(void)
  
  void __init arm64_memblock_init(void)
  {
-	const s64 linear_region_size = -(s64)PAGE_OFFSET;
+	const s64 linear_region_size = BIT(VA_BITS - 1);
  
  	/* Handle linux,usable-memory-range property */
  	fdt_enforce_memory_region();
@@ -362,13 +362,6 @@ void __init arm64_memblock_init(void)
  	/* Remove memory above our supported physical address size */
  	memblock_remove(1ULL << PHYS_MASK_SHIFT, ULLONG_MAX);
  
-	/*
-	 * Ensure that the linear region takes up exactly half of the kernel
-	 * virtual address space. This way, we can distinguish a linear address
-	 * from a kernel/module/vmalloc address by testing a single bit.
-	 */
-	BUILD_BUG_ON(linear_region_size != BIT(VA_BITS - 1));
-
  	/*
  	 * Select a suitable value for the base of physical memory.
  	 */
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 4b55b15707a3..ee5ec343d009 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -219,10 +219,10 @@ void __init kasan_init(void)
  	kasan_map_populate(kimg_shadow_start, kimg_shadow_end,
  			   early_pfn_to_nid(virt_to_pfn(lm_alias(_text))));
  
-	kasan_populate_early_shadow((void *)KASAN_SHADOW_START,
-				    (void *)mod_shadow_start);
+	kasan_populate_early_shadow(kasan_mem_to_shadow((void *) VA_START),
+				   (void *)mod_shadow_start);
  	kasan_populate_early_shadow((void *)kimg_shadow_end,
-				    kasan_mem_to_shadow((void *)PAGE_OFFSET));
+				   (void *)KASAN_SHADOW_END);
  
  	if (kimg_shadow_start > mod_shadow_end)
  		kasan_populate_early_shadow((void *)mod_shadow_end,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b6f5aa52ac67..7401a8481f78 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -389,7 +389,7 @@ static phys_addr_t pgd_pgtable_alloc(void)
  static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
  				  phys_addr_t size, pgprot_t prot)
  {
-	if (virt < VMALLOC_START) {
+	if ((virt >= VA_START) && (virt < VMALLOC_START)) {
  		pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
  			&phys, virt);
  		return;
@@ -416,7 +416,7 @@ void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
  static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
  				phys_addr_t size, pgprot_t prot)
  {
-	if (virt < VMALLOC_START) {
+	if ((virt >= VA_START) && (virt < VMALLOC_START)) {
  		pr_warn("BUG: not updating mapping for %pa at 0x%016lx - outside kernel range\n",
  			&phys, virt);
  		return;



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