Messages in this thread | | | From | Dan Williams <> | Date | Tue, 1 May 2018 20:20:49 -0700 | Subject | Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() |
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On Tue, May 1, 2018 at 8:13 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Tue, May 1, 2018 at 8:03 PM Dan Williams <dan.j.williams@intel.com> > wrote: > >> Because dax. There's no page cache indirection games we can play here >> to poison a page and map in another page. The mapped page is 1:1 >> associated with the filesystem block and physical memory address. > > I'm not talking page cache indirection. > > I'm talking literally mapping a different page into the kernel virtual > address space that the failing read was done for. > > But you seem to be right that we don't actually support that. I'm guessing > the hwpoison code has never had to run in that kind of situation and will > just give up. > > That would seem to be sad. It really feels like the obvious solution to any > MCE's - just map a dummy page at the address that causes problems. > > That can have bad effects for real memory (because who knows what internal > kernel data structure might be in there), but would seem to be the > _optimal_ solution for some random pmem access. And makes it absolutely > trivial to just return to the execution that got the error exception.
The other property of pmem that we need to contend with that makes it a snowflake relative to typical memory is that errors can be repaired by sending a slow-path command to the DIMM device. We trap block-layer writes in the pmem driver that target known 'badblocks' and send the sideband command to clear the error along with the new data.
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