diff options
| -rw-r--r-- | Documentation/arm64/tagged-pointers.txt | 34 | ||||
| -rw-r--r-- | arch/arm64/include/asm/pgtable-hwdef.h | 1 | ||||
| -rw-r--r-- | arch/arm64/kernel/entry.S | 1 | ||||
| -rw-r--r-- | arch/arm64/mm/proc.S | 2 |
4 files changed, 37 insertions, 1 deletions
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt new file mode 100644 index 000000000000..264e9841563a --- /dev/null +++ b/Documentation/arm64/tagged-pointers.txt @@ -0,0 +1,34 @@ + Tagged virtual addresses in AArch64 Linux + ========================================= + +Author: Will Deacon <will.deacon@arm.com> +Date : 12 June 2013 + +This document briefly describes the provision of tagged virtual +addresses in the AArch64 translation system and their potential uses +in AArch64 Linux. + +The kernel configures the translation tables so that translations made +via TTBR0 (i.e. userspace mappings) have the top byte (bits 63:56) of +the virtual address ignored by the translation hardware. This frees up +this byte for application use, with the following caveats: + + (1) The kernel requires that all user addresses passed to EL1 + are tagged with tag 0x00. This means that any syscall + parameters containing user virtual addresses *must* have + their top byte cleared before trapping to the kernel. + + (2) Tags are not guaranteed to be preserved when delivering + signals. This means that signal handlers in applications + making use of tags cannot rely on the tag information for + user virtual addresses being maintained for fields inside + siginfo_t. One exception to this rule is for signals raised + in response to debug exceptions, where the tag information + will be preserved. + + (3) Special care should be taken when using tagged pointers, + since it is likely that C compilers will not hazard two + addresses differing only in the upper bits. + +The architecture prevents the use of a tagged PC, so the upper byte will +be set to a sign-extension of bit 55 on exception return. diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h index e182a356c979..d57e66845c86 100644 --- a/arch/arm64/include/asm/pgtable-hwdef.h +++ b/arch/arm64/include/asm/pgtable-hwdef.h @@ -122,5 +122,6 @@ #define TCR_TG1_64K (UL(1) << 30) #define TCR_IPS_40BIT (UL(2) << 32) #define TCR_ASID16 (UL(1) << 36) +#define TCR_TBI0 (UL(1) << 37) #endif diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 57640df9d70c..3881fd115ebb 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -423,6 +423,7 @@ el0_da: * Data abort handling */ mrs x0, far_el1 + bic x0, x0, #(0xff << 56) disable_step x1 isb enable_dbg diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S index f84fcf71f129..b1b31bbc967b 100644 --- a/arch/arm64/mm/proc.S +++ b/arch/arm64/mm/proc.S @@ -147,7 +147,7 @@ ENTRY(__cpu_setup) * both user and kernel. */ ldr x10, =TCR_TxSZ(VA_BITS) | TCR_FLAGS | TCR_IPS_40BIT | \ - TCR_ASID16 | (1 << 31) + TCR_ASID16 | TCR_TBI0 | (1 << 31) #ifdef CONFIG_ARM64_64K_PAGES orr x10, x10, TCR_TG0_64K orr x10, x10, TCR_TG1_64K |