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| author | Catalin Marinas <catalin.marinas@arm.com> | 2015-07-10 17:24:28 +0100 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2015-07-27 11:08:39 +0100 |
| commit | 2f4b829c625ec36c2d80bef6395c7b74cea8aac0 (patch) | |
| tree | 806da0851ab4c8fd0ebda89d57e3b6057af66cef /arch/arm64/Kconfig | |
| parent | b08d4640a3dca68670fc5af2fe9205b395a02388 (diff) | |
| download | linux-2f4b829c625ec36c2d80bef6395c7b74cea8aac0.tar.gz linux-2f4b829c625ec36c2d80bef6395c7b74cea8aac0.tar.bz2 linux-2f4b829c625ec36c2d80bef6395c7b74cea8aac0.zip | |
arm64: Add support for hardware updates of the access and dirty pte bits
The ARMv8.1 architecture extensions introduce support for hardware
updates of the access and dirty information in page table entries. With
TCR_EL1.HA enabled, when the CPU accesses an address with the PTE_AF bit
cleared in the page table, instead of raising an access flag fault the
CPU sets the actual page table entry bit. To ensure that kernel
modifications to the page tables do not inadvertently revert a change
introduced by hardware updates, the exclusive monitor (ldxr/stxr) is
adopted in the pte accessors.
When TCR_EL1.HD is enabled, a write access to a memory location with the
DBM (Dirty Bit Management) bit set in the corresponding pte
automatically clears the read-only bit (AP[2]). Such DBM bit maps onto
the Linux PTE_WRITE bit and to check whether a writable (DBM set) page
is dirty, the kernel tests the PTE_RDONLY bit. In order to allow
read-only and dirty pages, the kernel needs to preserve the software
dirty bit. The hardware dirty status is transferred to the software
dirty bit in ptep_set_wrprotect() (using load/store exclusive loop) and
pte_modify().
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/Kconfig')
| -rw-r--r-- | arch/arm64/Kconfig | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 318175f62c24..40f717f8820a 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -469,6 +469,23 @@ config ARM64_VA_BITS default 42 if ARM64_VA_BITS_42 default 48 if ARM64_VA_BITS_48 +config ARM64_HW_AFDBM + bool "Support for hardware updates of the Access and Dirty page flags" + default y + help + The ARMv8.1 architecture extensions introduce support for + hardware updates of the access and dirty information in page + table entries. When enabled in TCR_EL1 (HA and HD bits) on + capable processors, accesses to pages with PTE_AF cleared will + set this bit instead of raising an access flag fault. + Similarly, writes to read-only pages with the DBM bit set will + clear the read-only bit (AP[2]) instead of raising a + permission fault. + + Kernels built with this configuration option enabled continue + to work on pre-ARMv8.1 hardware and the performance impact is + minimal. If unsure, say Y. + config CPU_BIG_ENDIAN bool "Build big-endian kernel" help |