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

[John Hubbard <jhubbard@xxxxxxxxxx>]

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.

And it *could* be so much more readable like this:

    dev_access_enable(DEV_ACCESS_THIS_THREAD);



thanks,
--
John Hubbard
NVIDIA