Messages in this thread | | | From | Dan Williams <> | Date | Mon, 4 May 2020 11:33:46 -0700 | Subject | Re: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe() |
| |
On Sun, May 3, 2020 at 5:57 AM David Laight <David.Laight@aculab.com> wrote: > > From: Linus Torvalds > > Sent: 01 May 2020 19:29 > ... > > And as DavidL pointed out - if you ever have "iomem" as a source or > > destination, you need yet another case. Not because they can take > > another kind of fault (although on some platforms you have the machine > > checks for that too), but because they have *very* different > > performance profiles (and the ERMS "rep movsb" sucks baby donkeys > > through a straw). > > > I was actually thinking that the nvdimm accesses need to be treated > much more like (cached) memory mapped io space than normal system > memory. > So treating them the same as "iomem" and then having access functions > that report access failures (which the current readq() doesn't) > might make sense.
While I agree that something like copy_mc_iomem_to_{user,kernel} could have users, nvdimm is not one of them.
> If you are using memory that 'might fail' for kernel code or data > you really get what you deserve.
nvdimms are no less "might fail" than DRAM, recall that some nvdimms are just DRAM with a platform promise that their contents are battery backed.
> OTOH system response to PCIe errors is currently rather problematic. > Mostly reads time out and return ~0u. > This can be checked for and, if possibly valid, a second location read.
Yes, the ambiguous ~0u return needs careful handling.
| |