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-rw-r--r--Documentation/arm64/tagged-pointers.txt34
-rw-r--r--arch/arm64/include/asm/pgtable-hwdef.h1
-rw-r--r--arch/arm64/kernel/entry.S1
-rw-r--r--arch/arm64/mm/proc.S2
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