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arm64: acpi: Map EFI_MEMORY_WT memory as Normal-NC
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>
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@ -239,6 +239,18 @@ done:
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}
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}
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static pgprot_t __acpi_get_writethrough_mem_attribute(void)
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{
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/*
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* Although UEFI specifies the use of Normal Write-through for
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* EFI_MEMORY_WT, it is seldom used in practice and not implemented
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* by most (all?) CPUs. Rather than allocate a MAIR just for this
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* purpose, emit a warning and use Normal Non-cacheable instead.
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*/
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pr_warn_once("No MAIR allocation for EFI_MEMORY_WT; treating as Normal Non-cacheable\n");
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return __pgprot(PROT_NORMAL_NC);
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}
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pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
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{
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/*
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@ -246,7 +258,7 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
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* types" of UEFI 2.5 section 2.3.6.1, each EFI memory type is
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* mapped to a corresponding MAIR attribute encoding.
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* The EFI memory attribute advises all possible capabilities
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* of a memory region. We use the most efficient capability.
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* of a memory region.
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*/
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u64 attr;
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@ -254,10 +266,10 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
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attr = efi_mem_attributes(addr);
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if (attr & EFI_MEMORY_WB)
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return PAGE_KERNEL;
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if (attr & EFI_MEMORY_WT)
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return __pgprot(PROT_NORMAL_WT);
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if (attr & EFI_MEMORY_WC)
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return __pgprot(PROT_NORMAL_NC);
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if (attr & EFI_MEMORY_WT)
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return __acpi_get_writethrough_mem_attribute();
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return __pgprot(PROT_DEVICE_nGnRnE);
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}
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@ -340,10 +352,10 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
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default:
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if (region->attribute & EFI_MEMORY_WB)
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prot = PAGE_KERNEL;
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else if (region->attribute & EFI_MEMORY_WT)
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prot = __pgprot(PROT_NORMAL_WT);
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else if (region->attribute & EFI_MEMORY_WC)
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prot = __pgprot(PROT_NORMAL_NC);
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else if (region->attribute & EFI_MEMORY_WT)
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prot = __acpi_get_writethrough_mem_attribute();
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}
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}
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return __ioremap(phys, size, prot);
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