Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v2] Powerpc/Watchpoint: Restore nvgprs while returning from exception | Date | Sun, 30 Jun 2019 18:37:27 +1000 (AEST) |
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On Thu, 2019-06-13 at 03:30:14 UTC, Ravi Bangoria wrote: > Powerpc hw triggers watchpoint before executing the instruction. To > make trigger-after-execute behavior, kernel emulates the instruction. > If the instruction is 'load something into non-volatile register', > exception handler should restore emulated register state while > returning back, otherwise there will be register state corruption. > Ex, Adding a watchpoint on a list can corrput the list: > > # cat /proc/kallsyms | grep kthread_create_list > c00000000121c8b8 d kthread_create_list > > Add watchpoint on kthread_create_list->prev: > > # perf record -e mem:0xc00000000121c8c0 > > Run some workload such that new kthread gets invoked. Ex, I just > logged out from console: > > list_add corruption. next->prev should be prev (c000000001214e00), \ > but was c00000000121c8b8. (next=c00000000121c8b8). > WARNING: CPU: 59 PID: 309 at lib/list_debug.c:25 __list_add_valid+0xb4/0xc0 > CPU: 59 PID: 309 Comm: kworker/59:0 Kdump: loaded Not tainted 5.1.0-rc7+ #69 > ... > NIP __list_add_valid+0xb4/0xc0 > LR __list_add_valid+0xb0/0xc0 > Call Trace: > __list_add_valid+0xb0/0xc0 (unreliable) > __kthread_create_on_node+0xe0/0x260 > kthread_create_on_node+0x34/0x50 > create_worker+0xe8/0x260 > worker_thread+0x444/0x560 > kthread+0x160/0x1a0 > ret_from_kernel_thread+0x5c/0x70 > > List corruption happened because it uses 'load into non-volatile > register' instruction: > > Snippet from __kthread_create_on_node: > > c000000000136be8: addis r29,r2,-19 > c000000000136bec: ld r29,31424(r29) > if (!__list_add_valid(new, prev, next)) > c000000000136bf0: mr r3,r30 > c000000000136bf4: mr r5,r28 > c000000000136bf8: mr r4,r29 > c000000000136bfc: bl c00000000059a2f8 <__list_add_valid+0x8> > > Register state from WARN_ON(): > > GPR00: c00000000059a3a0 c000007ff23afb50 c000000001344e00 0000000000000075 > GPR04: 0000000000000000 0000000000000000 0000001852af8bc1 0000000000000000 > GPR08: 0000000000000001 0000000000000007 0000000000000006 00000000000004aa > GPR12: 0000000000000000 c000007ffffeb080 c000000000137038 c000005ff62aaa00 > GPR16: 0000000000000000 0000000000000000 c000007fffbe7600 c000007fffbe7370 > GPR20: c000007fffbe7320 c000007fffbe7300 c000000001373a00 0000000000000000 > GPR24: fffffffffffffef7 c00000000012e320 c000007ff23afcb0 c000000000cb8628 > GPR28: c00000000121c8b8 c000000001214e00 c000007fef5b17e8 c000007fef5b17c0 > > Watchpoint hit at 0xc000000000136bec. > > addis r29,r2,-19 > => r29 = 0xc000000001344e00 + (-19 << 16) > => r29 = 0xc000000001214e00 > > ld r29,31424(r29) > => r29 = *(0xc000000001214e00 + 31424) > => r29 = *(0xc00000000121c8c0) > > 0xc00000000121c8c0 is where we placed a watchpoint and thus this > instruction was emulated by emulate_step. But because handle_dabr_fault > did not restore emulated register state, r29 still contains stale > value in above register state. > > Fixes: 5aae8a5370802 ("powerpc, hw_breakpoints: Implement hw_breakpoints for 64-bit server processors") > Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> > Cc: stable@vger.kernel.org # 2.6.36+
Applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/f474c28fbcbe42faca4eb415172c07d76adcb819
cheers
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