[V2] arm64/mm: Simplify and document pte_to_phys() for 52 bit addresses
Commit Message
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 <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
This applies on v6.1-rc4
Changes in V2:
- Added PTE_ADDR_HIGH_SHIFT based method per Ard
Changes in V1:
https://lore.kernel.org/all/20221031082421.1957288-1-anshuman.khandual@arm.com/
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(-)
Comments
Hello Anshuman,
On Mon, 7 Nov 2022 at 12:49, Anshuman Khandual
<anshuman.khandual@arm.com> 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().
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
With the nit below fixed, this looks good to me
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> This applies on v6.1-rc4
>
> Changes in V2:
>
> - Added PTE_ADDR_HIGH_SHIFT based method per Ard
>
> Changes in V1:
>
> https://lore.kernel.org/all/20221031082421.1957288-1-anshuman.khandual@arm.com/
>
> 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..6a39a3601cf7 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)
Please use tabs between the mnemonics and the arguments.
> #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
>
On 11/7/22 17:32, Ard Biesheuvel wrote:
> Hello Anshuman,
>
> On Mon, 7 Nov 2022 at 12:49, Anshuman Khandual
> <anshuman.khandual@arm.com> 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().
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Mark Brown <broonie@kernel.org>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Ard Biesheuvel <ardb@kernel.org>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>
> With the nit below fixed, this looks good to me
>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
>
>> ---
>> This applies on v6.1-rc4
>>
>> Changes in V2:
>>
>> - Added PTE_ADDR_HIGH_SHIFT based method per Ard
>>
>> Changes in V1:
>>
>> https://lore.kernel.org/all/20221031082421.1957288-1-anshuman.khandual@arm.com/
>>
>> 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..6a39a3601cf7 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)
>
> Please use tabs between the mnemonics and the arguments.
Sure, will do that.
@@ -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
@@ -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
@@ -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)