Re: [PATCH] pmem: export the symbols __copy_user_flushcache and __copy_from_user_flushcache

[Dan Williams]

On Wed, Sep 16, 2020 at 3:57 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
>
>
> On Tue, 15 Sep 2020, Mikulas Patocka wrote:
>
> >
> >
> > On Tue, 15 Sep 2020, Mikulas Patocka wrote:
> >
> > > > > - __copy_from_user_inatomic_nocache doesn't flush cache for leading and
> > > > > trailing bytes.
> > > >
> > > > You want copy_user_flushcache(). See how fs/dax.c arranges for
> > > > dax_copy_from_iter() to route to pmem_copy_from_iter().
> > >
> > > Is it something new for the kernel 5.10? I see only __copy_user_flushcache
> > > that is implemented just for x86 and arm64.
> > >
> > > There is __copy_from_user_flushcache implemented for x86, arm64 and power.
> > > It is used in lib/iov_iter.c under
> > > #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE - so should I use this?

Yes, but maybe not directly.

> > >
> > > Mikulas
> >
> > ... and __copy_user_flushcache is not exported for modules. So, I am stuck
> > with __copy_from_user_inatomic_nocache.
> >
> > Mikulas
>
> I'm submitting this patch that adds the required exports (so that we could
> use __copy_from_user_flushcache on x86, arm64 and powerpc). Please, queue
> it for the next merge window.

Why? This should go with the first user, and it's not clear that it
needs to be relative to the current dax_operations export scheme.

My first question about nvfs is how it compares to a daxfs with
executables and other binaries configured to use page cache with the
new per-file dax facility?