Nikunj A Dadhania <nik...@linux.vnet.ibm.com> writes: > Richard Henderson <r...@twiddle.net> writes: > >> On 09/12/2016 06:47 AM, Alex Bennée wrote: >>>> > + /* Notice an IO access, or a notdirty page. */ >>>> > + if (unlikely(tlb_addr & ~TARGET_PAGE_MASK)) { >>>> > + /* There's really nothing that can be done to >>>> > + support this apart from stop-the-world. */ >>>> > + goto stop_the_world; >>> We are also triggering on TLB_NOTDIRTY here in the case where a >>> conditional write is the first write to a page. I don't know if a >>> stop_the_world is required at this point but we will need to ensure we >>> clear bits as notdirty_mem_write() does. >>> >> >> You're quite right that we could probably special-case TLB_NOTDIRTY here such >> that (1) we needn't leave the cpu loop, and (2) needn't utilize the actual >> "write" part of notdirty_mem_write; just set the bits then fall through to >> the >> actual atomic instruction below. > > I do hit this case with ppc64, where I see that its the first write to > the page and it exits from this every time, causing the kernel to print > soft-lockups. > > Can we add the special case here for NOTDIRTY and set the page as dirty > and return successfully?
Does the atomic step fall-back not work for you? -- Alex Bennée