diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/arm64/tagged-pointers.txt | 62 | ||||
| -rw-r--r-- | Documentation/devicetree/bindings/clock/sunxi.txt | 2 | ||||
| -rw-r--r-- | Documentation/sysctl/fs.txt | 7 |
3 files changed, 56 insertions, 15 deletions
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt index d9995f1f51b3..a25a99e82bb1 100644 --- a/Documentation/arm64/tagged-pointers.txt +++ b/Documentation/arm64/tagged-pointers.txt @@ -11,24 +11,56 @@ 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: +this byte for application use. - (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) Non-zero tags are not 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 watchpoint debug exceptions, where the tag information - will be preserved. +Passing tagged addresses to the kernel +-------------------------------------- - (3) Special care should be taken when using tagged pointers, - since it is likely that C compilers will not hazard two - virtual addresses differing only in the upper byte. +All interpretation of userspace memory addresses by the kernel assumes +an address tag of 0x00. + +This includes, but is not limited to, addresses found in: + + - pointer arguments to system calls, including pointers in structures + passed to system calls, + + - the stack pointer (sp), e.g. when interpreting it to deliver a + signal, + + - the frame pointer (x29) and frame records, e.g. when interpreting + them to generate a backtrace or call graph. + +Using non-zero address tags in any of these locations may result in an +error code being returned, a (fatal) signal being raised, or other modes +of failure. + +For these reasons, passing non-zero address tags to the kernel via +system calls is forbidden, and using a non-zero address tag for sp is +strongly discouraged. + +Programs maintaining a frame pointer and frame records that use non-zero +address tags may suffer impaired or inaccurate debug and profiling +visibility. + + +Preserving tags +--------------- + +Non-zero tags are not 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 watchpoint debug exceptions, where the tag information will +be preserved. 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. + + +Other considerations +-------------------- + +Special care should be taken when using tagged pointers, since it is +likely that C compilers will not hazard two virtual addresses differing +only in the upper byte. diff --git a/Documentation/devicetree/bindings/clock/sunxi.txt b/Documentation/devicetree/bindings/clock/sunxi.txt index 8a47b77abfca..e8c74a6e738b 100644 --- a/Documentation/devicetree/bindings/clock/sunxi.txt +++ b/Documentation/devicetree/bindings/clock/sunxi.txt @@ -18,6 +18,7 @@ Required properties: "allwinner,sun4i-a10-cpu-clk" - for the CPU multiplexer clock "allwinner,sun4i-a10-axi-clk" - for the AXI clock "allwinner,sun8i-a23-axi-clk" - for the AXI clock on A23 + "allwinner,sun4i-a10-gates-clk" - for generic gates on all compatible SoCs "allwinner,sun4i-a10-axi-gates-clk" - for the AXI gates "allwinner,sun4i-a10-ahb-clk" - for the AHB clock "allwinner,sun5i-a13-ahb-clk" - for the AHB clock on A13 @@ -43,6 +44,7 @@ Required properties: "allwinner,sun6i-a31-apb0-gates-clk" - for the APB0 gates on A31 "allwinner,sun7i-a20-apb0-gates-clk" - for the APB0 gates on A20 "allwinner,sun8i-a23-apb0-gates-clk" - for the APB0 gates on A23 + "allwinner,sun8i-h3-apb0-gates-clk" - for the APB0 gates on H3 "allwinner,sun9i-a80-apb0-gates-clk" - for the APB0 gates on A80 "allwinner,sun4i-a10-apb1-clk" - for the APB1 clock "allwinner,sun9i-a80-apb1-clk" - for the APB1 bus clock on A80 diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt index 302b5ed616a6..35e17f748ca7 100644 --- a/Documentation/sysctl/fs.txt +++ b/Documentation/sysctl/fs.txt @@ -265,6 +265,13 @@ aio-nr can grow to. ============================================================== +mount-max: + +This denotes the maximum number of mounts that may exist +in a mount namespace. + +============================================================== + 2. /proc/sys/fs/binfmt_misc ---------------------------------------------------------- |