Re: [PATCH V11 4/5] arm64: apei: implement arch_apei_get_mem_attributes()

[Ard Biesheuvel]

On 11 August 2015 at 23:57, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, 08 Aug, at 10:18:52AM, Jonathan (Zhixiong) Zhang wrote:
>> From: "Jonathan (Zhixiong) Zhang" <zjzhang@xxxxxxxxxxxxxx>
>>
>> Table 8 of UEFI 2.5 section 2.3.6.1 defines mappings from EFI
>> memory types to MAIR attribute encodings for arm64.
>>
>> If the physical address has memory attributes defined by EFI
>> memmap as EFI_MEMORY_[UC|WC|WT], return approprate page protection
>> type according to the UEFI spec. Otherwise, return PAGE_KERNEL.
>>
>> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Acked-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
>> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@xxxxxxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/acpi.h | 30 ++++++++++++++++++++++++++++++
>>  1 file changed, 30 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
>> index 614096732839..b77a2d133da9 100644
>> --- a/arch/arm64/include/asm/acpi.h
>> +++ b/arch/arm64/include/asm/acpi.h
>> @@ -19,6 +19,11 @@
>>  #include <asm/psci.h>
>>  #include <asm/smp_plat.h>
>>
>> +#ifdef CONFIG_ACPI_APEI
>> +#include <linux/efi.h>
>> +#include <asm/pgtable.h>
>> +#endif
>> +
>>  /* Macros for consistency checks of the GICC subtable of MADT */
>>  #define ACPI_MADT_GICC_LENGTH        \
>>       (acpi_gbl_FADT.header.revision < 6 ? 76 : 80)
>> @@ -91,4 +95,29 @@ static inline const char *acpi_get_enable_method(int cpu)
>>  {
>>       return acpi_psci_present() ? "psci" : NULL;
>>  }
>> +
>> +#ifdef       CONFIG_ACPI_APEI
>> +static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
>> +{
>> +     /*
>> +      * According to "Table 8 Map: EFI memory types to AArch64 memory types"
>> +      * of UEFI 2.5 section 2.3.6.1, each EFI memory type is mapped to
>> +      * corresponding MAIR attribute encoding.
>> +      * The EFI memory attribute advises all possible capabilities of a
>> +      * memory region. We use the most efficient capability.
>> +      */
>> +
>> +     u64 attr;
>> +
>> +     attr = efi_mem_attributes(addr);
>> +     if (attr & EFI_MEMORY_WB)
>> +             return PAGE_KERNEL;
>> +     if (attr & EFI_MEMORY_WT)
>> +             return __pgprot(PROT_NORMAL_WT);
>> +     if (attr & EFI_MEMORY_WC)
>> +             return __pgprot(PROT_NORMAL_NC);
>> +     return __pgprot(PROT_DEVICE_nGnRnE);
>> +}
>> +#endif
>> +
>>  #endif /*_ASM_ACPI_H*/
>
> Everyone happy with this change? Ard?
>

Yes, this looks fine. As long as any region that has the EFI_MEMORY_WB
attribute gets mapped as PAGE_KERNEL, we know we won't be violating
any architectural mismatched attributes constraints (since all
EFI_MEMORY_WB regions, even the occupied ones, are covered by the
kernel direct mapping as well)

For the other ones, it is merely an optimization, but arguably still
an improvement.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

Thanks,
Ard.
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