* Linus Torvalds <[email protected]> wrote:
> On Wed, Feb 24, 2016 at 11:27 AM, Tony Luck <[email protected]> wrote:
> >
> > This isn't just about NVDIMMs. It is about uncorrected errors in any
> > type of memory.
> >
> > The copy_from_user() case I'd like to fix is when there is an uncorrected
> > in
> > memory. This can happen to regular DDR3/DDR4 memory just as it can happen
> > to
> > NVDIMM. When a user process directly reads the location with the
> > uncorrected
> > error the h/w triggers a machine check and if the error is marked as
> > recoverable the kernel will SIGBUS the process. See mm/memory-failure.c
>
> But the way to fix that is absolutely *not* to introduce some new concept.
>
> You'd just extend the _existing_ get_user() and put_user() functions to
> return a
> different error code for a memory error. Instead of -EFAULT, maybe they can
> return -EMEMERR or something.
>
> I do not see how it could possibly ever make sense to introduce a new name
> and
> then make old users use that new name instead.
So if we do that we should first fix these hard coded assumptions about uaccess
return codes:
triton:~/tip> git grep -E '== -EFAULT' | wc -l
44
But yes, your suggestion sounds a lot cleaner and a lot more powerful overall.
AFAICS we'll still need this exception table extension commit:
548acf19234d x86/mm: Expand the exception table logic to allow new handling
options
to propagate the error code to actual uaccess methods, right?
Alternatively we could change the exception handling protocol and change _all_
uaccess methods all at once, but I think that would be crazy complex and risky.
I'd rather change key uaccess methods step by step.
So if everyone agrees then I'll keep this commit queued up. The followup
patches
will have to be reworked according to Linus's suggestions.
Thanks,
Ingo
