[PATCH 5.9 572/757] arm64: mm: use single quantity to represent the PA to VA translation

Greg Kroah-Hartman
2020-10-27T16:39:48Z

From: Ard Biesheuvel <ardb@kernel.org>

[ Upstream commit 7bc1a0f9e1765830e945669c99c59c35cf9bca82 ]

On arm64, the global variable memstart_addr represents the physical
address of PAGE_OFFSET, and so physical to virtual translations or
vice versa used to come down to simple additions or subtractions
involving the values of PAGE_OFFSET and memstart_addr.

When support for 52-bit virtual addressing was introduced, we had to
deal with PAGE_OFFSET potentially being outside of the region that
can be covered by the virtual range (as the 52-bit VA capable build
needs to be able to run on systems that are only 48-bit VA capable),
and for this reason, another translation was introduced, and recorded
in the global variable physvirt_offset.

However, if we go back to the original definition of memstart_addr,
i.e., the physical address of PAGE_OFFSET, it turns out that there is
no need for two separate translations: instead, we can simply subtract
the size of the unaddressable VA space from memstart_addr to make the
available physical memory appear in the 48-bit addressable VA region.

This simplifies things, but also fixes a bug on KASLR builds, which
may update memstart_addr later on in arm64_memblock_init(), but fails
to update vmemmap and physvirt_offset accordingly.

Fixes: 5383cc6efed1 ("arm64: mm: Introduce vabits_actual")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Link: https://lore.kernel.org/r/20201008153602.9467-2-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/memory.h | 5 ++---
arch/arm64/include/asm/pgtable.h | 4 ++--
arch/arm64/mm/init.c | 30 ++++++++++--------------------
3 files changed, 14 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index afa722504bfde..1ded73189874d 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -164,7 +164,6 @@
extern u64 vabits_actual;
#define PAGE_END (_PAGE_END(vabits_actual))

-extern s64 physvirt_offset;
extern s64 memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
#define PHYS_OFFSET ({ VM_BUG_ON(memstart_addr & 1); memstart_addr; })
@@ -240,7 +239,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
*/
#define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1)))

-#define __lm_to_phys(addr) (((addr) + physvirt_offset))
+#define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
#define __kimg_to_phys(addr) ((addr) - kimage_voffset)

#define __virt_to_phys_nodebug(x) ({ \
@@ -258,7 +257,7 @@ extern phys_addr_t __phys_addr_symbol(unsigned long x);
#define __phys_addr_symbol(x) __pa_symbol_nodebug(x)
#endif /* CONFIG_DEBUG_VIRTUAL */

-#define __phys_to_virt(x) ((unsigned long)((x) - physvirt_offset))
+#define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
#define __phys_to_kimg(x) ((unsigned long)((x) + kimage_voffset))

/*
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index d5d3fbe739534..88233d42d9c29 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -23,6 +23,8 @@
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (- PUD_SIZE - VMEMMAP_SIZE - SZ_64K)

+#define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
+
#define FIRST_USER_ADDRESS 0UL

#ifndef __ASSEMBLY__
@@ -33,8 +35,6 @@
#include <linux/mm_types.h>
#include <linux/sched.h>

-extern struct page *vmemmap;
-
extern void __pte_error(const char *file, int line, unsigned long val);
extern void __pmd_error(const char *file, int line, unsigned long val);
extern void __pud_error(const char *file, int line, unsigned long val);
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 481d22c32a2e7..324f0e0894f6e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -54,12 +54,6 @@
s64 memstart_addr __ro_after_init = -1;
EXPORT_SYMBOL(memstart_addr);

-s64 physvirt_offset __ro_after_init;
-EXPORT_SYMBOL(physvirt_offset);
-
-struct page *vmemmap __ro_after_init;
-EXPORT_SYMBOL(vmemmap);
-
/*
* We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA covers the first 1G of
* memory as some devices, namely the Raspberry Pi 4, have peripherals with
@@ -290,20 +284,6 @@ void __init arm64_memblock_init(void)
memstart_addr = round_down(memblock_start_of_DRAM(),
ARM64_MEMSTART_ALIGN);

- physvirt_offset = PHYS_OFFSET - PAGE_OFFSET;
-
- vmemmap = ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT));
-
- /*
- * If we are running with a 52-bit kernel VA config on a system that
- * does not support it, we have to offset our vmemmap and physvirt_offset
- * s.t. we avoid the 52-bit portion of the direct linear map
- */
- if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52)) {
- vmemmap += (_PAGE_OFFSET(48) - _PAGE_OFFSET(52)) >> PAGE_SHIFT;
- physvirt_offset = PHYS_OFFSET - _PAGE_OFFSET(48);
- }
-
/*
* Remove the memory that we will not be able to cover with the
* linear mapping. Take care not to clip the kernel which may be
@@ -318,6 +298,16 @@ void __init arm64_memblock_init(void)
memblock_remove(0, memstart_addr);
}

+ /*
+ * If we are running with a 52-bit kernel VA config on a system that
+ * does not support it, we have to place the available physical
+ * memory in the 48-bit addressable part of the linear region, i.e.,
+ * we have to move it upward. Since memstart_addr represents the
+ * physical address of PAGE_OFFSET, we have to *subtract* from it.
+ */
+ if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
+ memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
+
/*
* Apply the memory limit if it was set. Since the kernel may be loaded
* high up in memory, add back the kernel region that must be accessible
--
2.25.1