Re: [PATCH RFC PKS/PMEM 57/58] nvdimm/pmem: Stray access protection for pmem->virt_addr

[Ira Weiny <ira.weiny@xxxxxxxxx>]

On Fri, Oct 09, 2020 at 07:53:07PM -0700, John Hubbard wrote:
> On 10/9/20 12:50 PM, ira.weiny@xxxxxxxxx wrote:
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> > 
> > The pmem driver uses a cached virtual address to access its memory
> > directly.  Because the nvdimm driver is well aware of the special
> > protections it has mapped memory with, we call dev_access_[en|dis]able()
> > around the direct pmem->virt_addr (pmem_addr) usage instead of the
> > unnecessary overhead of trying to get a page to kmap.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> > ---
> >   drivers/nvdimm/pmem.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index fab29b514372..e4dc1ae990fc 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -148,7 +148,9 @@ static blk_status_t pmem_do_read(struct pmem_device 
> > *pmem,
> >     if (unlikely(is_bad_pmem(&pmem->bb, sector, len)))
> >             return BLK_STS_IOERR;
> > +   dev_access_enable(false);
> >     rc = read_pmem(page, page_off, pmem_addr, len);
> > +   dev_access_disable(false);
> 
> Hi Ira!
> 
> The APIs should be tweaked to use a symbol (GLOBAL, PER_THREAD), instead of
> true/false. Try reading the above and you'll see that it sounds like it's
> doing the opposite of what it is ("enable_this(false)" sounds like a clumsy
> API design to *disable*, right?). And there is no hint about the scope.

Sounds reasonable.

> 
> And it *could* be so much more readable like this:
> 
>     dev_access_enable(DEV_ACCESS_THIS_THREAD);

I'll think about the flag name.  I'm not liking 'this thread'.

Maybe DEV_ACCESS_[GLOBAL|THREAD]

Ira