On 6/21/2017 11:59 AM, Borislav Petkov wrote:
On Wed, Jun 21, 2017 at 05:37:22PM +0200, Joerg Roedel wrote:
Do you mean this is like the last exception case in that document above:
"
- Pointers to data structures in coherent memory which might be modified
by I/O devices can, sometimes, legitimately be volatile. A ring buffer
used by a network adapter, where that adapter changes pointers to
indicate which descriptors have been processed, is an example of this
type of situation."
?
So currently (without this patch) the build_completion_wait function
does not take a volatile parameter, only wait_on_sem() does.
Wait_on_sem() needs it because its purpose is to poll a memory location
which is changed by the iommu-hardware when its done with command
processing.
Right, the reason above - memory modifiable by an IO device. You could
add a comment there explaining the need for the volatile.
But the 'volatile' in build_completion_wait() looks unnecessary, because
the function does not poll the memory location. It only uses the
pointer, converts it to a physical address and writes it to the command
to be queued.
Ok.
Ok, so the (now) current version of the patch that doesn't change the
function signature is the right way to go.
Thanks,
Tom
Thanks.
