On Thu, Jun 29, 2017 at 10:53 AM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > There's a bug here that will need a small change to the entry code. > > Mike Galbraith reported: > > WARNING: can't dereference registers at ffffc900089d7e08 for ip > ffffffff81740bbb > > After some looking I found that it's caused by the following code > snippet in the 'interrupt' macro in entry_64.S: > > /* > * Save previous stack pointer, optionally switch to interrupt stack. > * irq_count is used to check if a CPU is already on an interrupt > stack > * or not. While this is essentially redundant with preempt_count it > is > * a little cheaper to use a separate counter in the PDA (short of > * moving irq_enter into assembly, which would be too much work) > */ > movq %rsp, %rdi > incl PER_CPU_VAR(irq_count) > cmovzq PER_CPU_VAR(irq_stack_ptr), %rsp > UNWIND_HINT_REGS base=rdi > pushq %rdi > UNWIND_HINT_REGS indirect=1 > > The problem is that it's changing the stack pointer *before* writing the > previous stack pointer (push %rdi). So when unwinding from an NMI which > hit between the rsp write and the rdi push, the unwinder tries to access > the regs on the previous stack (by reading rdi), but the previous stack > pointer isn't there yet, so the access is considered out of bounds.
Ugh, that code. Does this problem go away with this patch applied: https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_ist&id=2231ec7e0bcc1a2bc94a17081511ab54cc6badd1 If so, want to update the patch for new kernels (shouldn't conflict with anything except your unwind hints)? --Andy
