From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: kernel-team@android.com, Will Deacon <will@kernel.org>,
Christoph Hellwig <hch@lst.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: [PATCH v2 2/3] arm64: acpi: Map EFI_MEMORY_WT memory as Normal-NC
Date: Thu, 27 May 2021 12:03:18 +0100 [thread overview]
Message-ID: <20210527110319.22157-3-will@kernel.org> (raw)
In-Reply-To: <20210527110319.22157-1-will@kernel.org>
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>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kernel/acpi.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index cada0b816c8a..f3851724fe35 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -239,6 +239,18 @@ void __init acpi_boot_table_init(void)
}
}
+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);
--
2.31.1.818.g46aad6cb9e-goog
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next prev parent reply other threads:[~2021-05-27 11:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-27 11:03 [PATCH v2 0/3] Free up a couple of MAIRs Will Deacon
2021-05-27 11:03 ` [PATCH v2 1/3] arm64: mm: Remove unused support for Device-GRE memory type Will Deacon
2021-05-27 11:03 ` Will Deacon [this message]
2021-05-27 11:03 ` [PATCH v2 3/3] arm64: mm: Remove unused support for Normal-WT " Will Deacon
2021-06-01 18:21 ` [PATCH v2 0/3] Free up a couple of MAIRs Will Deacon
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