On Fri, Dec 17, 2021 at 12:45:45PM -0800, Linus Torvalds wrote:
On Fri, Dec 17, 2021 at 12:42 PM David Hildenbrand david@redhat.com wrote:
Then somebody else modified that page, and you got exactly what you asked for - a COW event. The original R/O pin has the original page that it asked for, and can read it just fine.
Where in the code did I ask for a COW event? I asked for a R/O pin, not any kind of memory protection.
Why didn't you ask for a shared pin, if that is what you want?
We already support that.
If you don't like the read-only pins, don't use them. It's that simple.
So you are saying that if a GUP user wants to see changes made by userspace to the page after the GUP it must ask for FOLL_WRITE, even if it doesn't have intend to write to the page?
That's news to me.
Or did I misunderstand you?