2022-11-07 14:37:53

by Anshuman Khandual

Subject: [PATCH V3] arm64/mm: Simplify and document pte_to_phys() for 52 bit addresses

pte_to_phys() assembly definition does multiple bits field transformations
to derive physical address, embedded inside a page table entry. Unlike its
C counter part i.e __pte_to_phys(), pte_to_phys() is not very apparent. It
simplifies these operations via a new macro PTE_ADDR_HIGH_SHIFT indicating
how far the pte encoded higher address bits need to be left shifted. While
here, this also updates __pte_to_phys() and __phys_to_pte_val().

Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Ard Biesheuvel <[email protected]>
Suggested-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Anshuman Khandual <[email protected]>
---
This applies on v6.1-rc4

Changes in V3:

- Added tab after the mnemonics per Ard

Changes in V2:

https://lore.kernel.org/all/[email protected]/

- Added PTE_ADDR_HIGH_SHIFT based method per Ard

Changes in V1:

https://lore.kernel.org/all/[email protected]/


arch/arm64/include/asm/assembler.h | 8 +++-----
arch/arm64/include/asm/pgtable-hwdef.h | 1 +
arch/arm64/include/asm/pgtable.h | 4 ++--
3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index e5957a53be39..89038067ef34 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -660,12 +660,10 @@ alternative_endif
.endm

.macro pte_to_phys, phys, pte
-#ifdef CONFIG_ARM64_PA_BITS_52
- ubfiz \phys, \pte, #(48 - 16 - 12), #16
- bfxil \phys, \pte, #16, #32
- lsl \phys, \phys, #16
-#else
and \phys, \pte, #PTE_ADDR_MASK
+#ifdef CONFIG_ARM64_PA_BITS_52
+ orr \phys, \phys, \phys, lsl #PTE_ADDR_HIGH_SHIFT
+ and \phys, \phys, GENMASK_ULL(PHYS_MASK_SHIFT - 1, PAGE_SHIFT)
#endif
.endm

diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index 5ab8d163198f..f658aafc47df 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -159,6 +159,7 @@
#ifdef CONFIG_ARM64_PA_BITS_52
#define PTE_ADDR_HIGH (_AT(pteval_t, 0xf) << 12)
#define PTE_ADDR_MASK (PTE_ADDR_LOW | PTE_ADDR_HIGH)
+#define PTE_ADDR_HIGH_SHIFT 36
#else
#define PTE_ADDR_MASK PTE_ADDR_LOW
#endif
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 71a1af42f0e8..daedd6172227 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -77,11 +77,11 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
static inline phys_addr_t __pte_to_phys(pte_t pte)
{
return (pte_val(pte) & PTE_ADDR_LOW) |
- ((pte_val(pte) & PTE_ADDR_HIGH) << 36);
+ ((pte_val(pte) & PTE_ADDR_HIGH) << PTE_ADDR_HIGH_SHIFT);
}
static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
{
- return (phys | (phys >> 36)) & PTE_ADDR_MASK;
+ return (phys | (phys >> PTE_ADDR_HIGH_SHIFT)) & PTE_ADDR_MASK;
}
#else
#define __pte_to_phys(pte) (pte_val(pte) & PTE_ADDR_MASK)
--
2.25.1

2022-11-09 20:04:16

by Will Deacon

Subject: Re: [PATCH V3] arm64/mm: Simplify and document pte_to_phys() for 52 bit addresses

On Mon, 7 Nov 2022 19:47:53 +0530, Anshuman Khandual wrote:
> pte_to_phys() assembly definition does multiple bits field transformations
> to derive physical address, embedded inside a page table entry. Unlike its
> C counter part i.e __pte_to_phys(), pte_to_phys() is not very apparent. It
> simplifies these operations via a new macro PTE_ADDR_HIGH_SHIFT indicating
> how far the pte encoded higher address bits need to be left shifted. While
> here, this also updates __pte_to_phys() and __phys_to_pte_val().
>
> [...]

Applied to arm64 (for-next/mm), thanks!

[1/1] arm64/mm: Simplify and document pte_to_phys() for 52 bit addresses
https://git.kernel.org/arm64/c/a4ee28615c7a

Cheers,
--
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev