On Thu, 27 Jul 2023 at 10:03, Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> wrote: > On 7/27/23 2:10 AM, Michał Mirosław wrote: > > On Wed, 26 Jul 2023 at 10:34, Muhammad Usama Anjum > > <usama.anjum@xxxxxxxxxxxxx> wrote: > >> On 7/25/23 11:05 PM, Michał Mirosław wrote: > >>> On Tue, 25 Jul 2023 at 11:11, Muhammad Usama Anjum > >>> <usama.anjum@xxxxxxxxxxxxx> wrote: [...] > >>> 2. For the address tagging part I'd prefer someone who knows how this > >>> is used take a look. We're ignoring the tag (but clear it on return in > >>> ->start) - so it doesn't matter for the ioctl() itself. > >> I've added Kirill if he can give his thoughts about tagged memory. > >> > >> Right now we are removing the tags from all 3 pointers (start, end, vec) > >> before using the pointers on kernel side. But we are overwriting and > >> writing the walk ending address in start which user can read/use. > >> > >> I think we shouldn't over-write the start (and its tag) and instead return > >> the ending walk address in new variable, walk_end. > > > > The overwrite of `start` is making the ioctl restart (continuation) > > easier to handle. I prefer the current way, but it's not a strong > > opinion. > We shouldn't overwrite the start if we aren't gonna put the correct tag. So > I've resorted to adding another variable `walk_end` to return the walk > ending address. Yes. We have two options: 1. add new field and have the userspace check it and update start itself to continue the scan, or: 2. reconstruct the tag from either orignal `start` or `end` and have the userspace re-set `start` if it wants to restart the scan instead of continuing. (the second one, using `end`'s tag, might be the easiest for userspace, as it can check `start` == `end` when deciding to continue or restart). Best Regards Michał Mirosław
