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Date: Thu, 06 Jun 2019 13:51:20 +0530 From: "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com> To: mpe@...erman.id.au, Ravi Bangoria <ravi.bangoria@...ux.ibm.com> Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, mahesh@...ux.vnet.ibm.com, mikey@...ling.org, npiggin@...il.com, paulus@...ba.org Subject: Re: [PATCH] Powerpc/Watchpoint: Restore nvgprs while returning from exception 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->next: > > # 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 > > Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com> > --- > arch/powerpc/kernel/exceptions-64s.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > Awesome catch - this one has had a glorious run... Fixes: 5aae8a5370802 ("powerpc, hw_breakpoints: Implement hw_breakpoints for 64-bit server processors") Reviewed-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com> - Naveen
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