On Mon, Dec 24, 2018 at 04:32:39PM +0800, Jason Wang wrote:
On 2018/12/14 äå8:33, Michael S. Tsirkin wrote:
On Fri, Dec 14, 2018 at 11:42:18AM +0800, Jason Wang wrote:
On 2018/12/13 äå11:27, Michael S. Tsirkin wrote:I mean the next barrier people decide to put into userspace
On Thu, Dec 13, 2018 at 06:10:19PM +0800, Jason Wang wrote:I don't get here, do you mean spec barriers?
Hi:Userspace accesses through remapping tricks and next time there's a need
This series tries to access virtqueue metadata through kernel virtual
address instead of copy_user() friends since they had too much
overheads like checks, spec barriers or even hardware feature
for a new barrier we are left to figure it out by ourselves.
It's completely unnecessary forIt's defence in depth. Take a look at the commit that added them.
vhost which is kernel thread.
And yes quite possibly in most cases we actually have a spec
barrier in the validation phase. If we do let's use the
unsafe variants so they can be found.
unsafe variants can only work if you can batch userspace access. This is not
necessarily the case for light load.
Do we care a lot about the light load? How would you benchmark it?
It doesn't matter really, if you dirty pages behind the MM backAnd even if you're right, vhost is not theFor sure. But if one can get by without get user pages, one
only place, there's lots of vmap() based accessing in kernel.
really should. Witness recently uncovered mess with file
We only pin metadata pages, I don't believe they will be used by any DMA.
the problem is there.