diff mbox series

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

Message ID 20201009195033.3208459-58-ira.weiny@intel.com
State New
Headers show
Series PMEM: Introduce stray write protection for PMEM | expand

Commit Message

Ira Weiny Oct. 9, 2020, 7:50 p.m. UTC
From: Ira Weiny <ira.weiny@intel.com>

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@intel.com>
---
 drivers/nvdimm/pmem.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

John Hubbard Oct. 10, 2020, 2:53 a.m. UTC | #1
On 10/9/20 12:50 PM, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> 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@intel.com>
> ---
>   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,
Ira Weiny Oct. 12, 2020, 5:52 a.m. UTC | #2
On Fri, Oct 09, 2020 at 07:53:07PM -0700, John Hubbard wrote:
> On 10/9/20 12:50 PM, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> > 
> > 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@intel.com>
> > ---
> >   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
diff mbox series

Patch

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);
 	flush_dcache_page(page);
 	return rc;
 }
@@ -180,11 +182,13 @@  static blk_status_t pmem_do_write(struct pmem_device *pmem,
 	 * after clear poison.
 	 */
 	flush_dcache_page(page);
+	dev_access_enable(false);
 	write_pmem(pmem_addr, page, page_off, len);
 	if (unlikely(bad_pmem)) {
 		rc = pmem_clear_poison(pmem, pmem_off, len);
 		write_pmem(pmem_addr, page, page_off, len);
 	}
+	dev_access_disable(false);
 
 	return rc;
 }