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arm64: acpi: Map EFI_MEMORY_WT memory as Normal-NC

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The only user we have of Normal Write-Through memory is in the ACPI code
when mapping memory regions advertised as EFI_MEMORY_WT. Since most (all?)
CPUs treat write-through as non-cacheable under the hood, don't bother
with the extra memory type here and just treat EFI_MEMORY_WT the same way
as EFI_MEMORY_WC by mapping it to the Normal-NC memory type instead and
emitting a warning if we have failed to find an alternative EFI memory
type.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210527110319.22157-3-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2021-05-27 12:03:18 +01:00
parent 58cc6b72a2
commit ee67c1103a
1 changed files with 17 additions and 5 deletions
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22
arch/arm64/kernel/acpi.c
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@ -239,6 +239,18 @@ done:
}
}
static pgprot_t __acpi_get_writethrough_mem_attribute(void)
{
/*
* Although UEFI specifies the use of Normal Write-through for
* EFI_MEMORY_WT, it is seldom used in practice and not implemented
* by most (all?) CPUs. Rather than allocate a MAIR just for this
* purpose, emit a warning and use Normal Non-cacheable instead.
*/
pr_warn_once("No MAIR allocation for EFI_MEMORY_WT; treating as Normal Non-cacheable\n");
return __pgprot(PROT_NORMAL_NC);
}
pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
{
/*
@ -246,7 +258,7 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
* types" of UEFI 2.5 section 2.3.6.1, each EFI memory type is
* mapped to a corresponding MAIR attribute encoding.
* The EFI memory attribute advises all possible capabilities
* of a memory region. We use the most efficient capability.
* of a memory region.
*/
u64 attr;
@ -254,10 +266,10 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
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);
if (attr & EFI_MEMORY_WT)
return __acpi_get_writethrough_mem_attribute();
return __pgprot(PROT_DEVICE_nGnRnE);
}
@ -340,10 +352,10 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
default:
if (region->attribute & EFI_MEMORY_WB)
prot = PAGE_KERNEL;
else if (region->attribute & EFI_MEMORY_WT)
prot = __pgprot(PROT_NORMAL_WT);
else if (region->attribute & EFI_MEMORY_WC)
prot = __pgprot(PROT_NORMAL_NC);
else if (region->attribute & EFI_MEMORY_WT)
prot = __acpi_get_writethrough_mem_attribute();
}
}
return __ioremap(phys, size, prot);