user/sven/linux.git/arch/arc/kernel/process.c, branch v4.20

ARC: clone syscall to setp r25 as thread pointer

2018-10-05T21:33:29Z

Per ARC TLS ABI, r25 is designated TP (thread pointer register). However so far kernel didn't do any special treatment, like setting up usermode r25, even for CLONE_SETTLS. We instead relied on libc runtime to do this, in say clone libc wrapper [1]. This was deliberate to keep kernel ABI agnostic (userspace could potentially change TP, specially for different ARC ISA say ARCompact vs. ARCv2 with different spare registers etc) However userspace setting up r25, after clone syscall opens a race, if child is not scheduled and gets a signal instead. It starts off in userspace not in clone but in a signal handler and anything TP sepcific there such as pthread_self() fails which showed up with uClibc testsuite nptl/tst-kill6 [2] Fix this by having kernel populate r25 to TP value. So this locks in ABI, but it was not going to change anyways, and fwiw is same for both ARCompact (arc700 core) and ARCvs (HS3x cores) [1] https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/sysdeps/linux/arc/clone.S [2] https://github.com/wbx-github/uclibc-ng-test/blob/master/test/nptl/tst-kill6.c Fixes: ARC STAR 9001378481 Cc: stable@vger.kernel.org Reported-by: Nikita Sobolev Signed-off-by: Vineet Gupta

ARC: Improve cmpxchg syscall implementation

2018-07-09T18:22:05Z

This is used in configs lacking hardware atomics to emulate atomic r-m-w for user space, implemented by disabling preemption in kernel. However there are issues in current implementation: 1. Process not terminated if invalid user pointer passed: i.e. __get_user() failed. 2. The reason for this patch was __put_user() failure not being handled either, specifically for the COW break scenario. The zero page is initially wired up and read from __get_user() succeeds. A subsequent write by __put_user() induces a Protection Violation, but COW can't finish as Linux page fault handler is disabled due to preempt disable. And what's worse is we silently return the stale value to user space. Fix this specific case by re-enabling preemption and explicitly fixing up the fault and retrying the whole sequence over. Cc: Max Filippov Cc: linux-arch@vger.kernel.org Signed-off-by: Alexey Brodkin Signed-off-by: Peter Zijlstra Signed-off-by: Vineet Gupta [vgupta: rewrote the changelog]

ARC: [plat-eznps] handle extra aux regs #2: kernel/entry exit

2017-08-28T22:17:36Z

Preserve eflags and gpa1 aux during entry/exit into kernel as these could be modified by kernel mode These registers used by compare exchange instructions. - GPA1 is used for compare value, - EFLAGS got bit reflects atomic operation response. EFLAGS is zeroed for each new user task so it won't get its parent value. Signed-off-by: Liav Rehana Signed-off-by: Noam Camus Signed-off-by: Vineet Gupta

ARC: [plat-eznps] use schd.wft instruction instead of sleep at idle task

2017-08-28T22:17:36Z

When HW threads are active we want CPU to enter idle state only for the calling HW thread and not to put on sleep all HW threads sharing this core. For this need the NPS400 got dedicated instruction so only calling thread is entring sleep and all other are still awake and can execute instructions. Signed-off-by: Noam Camus Signed-off-by: Vineet Gupta [vgupta: reworked patch to not use inline ifdef but a new function itself]

ARC: create cpu specific version of arch_cpu_idle()

2017-08-28T22:17:36Z

This paves way for creating a 3rd variant needed for NPS ARC700 without littering ifdey'ery all over the place Signed-off-by: Vineet Gupta

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:36Z

We are going to split out of , which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:35Z

ARC: change return value of userspace cmpxchg assist syscall

2016-11-07T19:01:12Z

The original syscall only used to return errno to indicate if cmpxchg succeeded. It was not returning the "previous" value which typical cmpxchg callers are interested in to build their slowpaths or retry loops. Given user preemption in syscall return path etc, it is not wise to check this in userspace afterwards, but should be what kernel actually observed in the syscall. So change the syscall interface to always return the previous value and additionally set Z flag to indicate whether operation succeeded or not (just like ARM implementation when they used to have this syscall) The flag approach avoids having to put_user errno which is nice given the use case for this syscall cares mostly about the "previous" value. Signed-off-by: Vineet Gupta

ARC: syscall for userspace cmpxchg assist

2016-10-24T16:24:26Z

Older ARC700 cores (ARC750 specifically) lack instructions to implement atomic r-w-w. This is problematic for userspace libraries such as NPTL which need atomic primitives. So enable them by providing kernel assist. This is costly but really the only sane soluton (othern than tight spinning using the otherwise availiable atomic exchange EX instruciton). Good thing is there are only a few of these cores running Linux out in the wild. This only works on UP systems. Reviewed-by: Colin Ian King Signed-off-by: Vineet Gupta

ARC: Support syscall ABI v4

2016-08-19T17:44:34Z

The syscall ABI includes the gcc functional calling ABI since a syscall implies userland caller and kernel callee. The current gcc ABI (v3) for ARCv2 ISA required 64-bit data be passed in even-odd register pairs, (potentially punching reg holes when passing such values as args). This was partly driven by the fact that the double-word LDD/STD instructions in ARCv2 expect the register alignment and thus gcc forcing this avoids extra MOV at the cost of a few unused register (which we have plenty anyways). This however was rejected as part of upstreaming gcc port to HS. So the new ABI v4 doesn't enforce the even-odd reg restriction. Do note that for ARCompact ISA builds v3 and v4 are practically the same in terms of gcc code generation. In terms of change management, we infer the new ABI if gcc 6.x onwards is used for building the kernel. This also needs a stable backport to enable older kernels to work with new tools/user-space Cc: Signed-off-by: Vineet Gupta