Stephen C. Tweedie wrote:
So... the interface (a) cannot be used on the Linux VM without at least one invasive VM modification, due to the requirement of ptes being explicitly unmapped via hypercall;
Also there is the use of VM_FOREIGN (http://xenbits.xensource.com/linux-2.6.18-xen.hg?file/b2768401db94/mm/memory.c lines 1040--1059), which has been used quite happily in blktap since 2005 (http://lists.xensource.com/archives/html/xen-changelog/2005-07/msg00053.html). While it may not be a priority to get gntdev into pv-ops Linux, I should imagine that blktap would be fairly critical.
I can't help wondering if this is a hint that now is the time to find a better API, which doesn't have the requirement (a) that seems to be causing such trouble? Are other PV guests --- *BSD, Solaris --- going to have the same problems with their VM layers if they try to implement this API? Upstream Linux pv_ops certainly will, and it would be good if we could avoid tying unprivileged guests to ABIs which cannot hope to be merged into pv_ops.
I'm open to suggestions... but I think it always reduces to needing a hook that is called on process exit before the PTEs are zapped.
(Just what is the cost of not having this functionality in blktap, anyway?)
If tapdisk dies whilst holding a granted page, the page can never be ungranted, so we leak that page.
Regards, Derek. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/virtualization
