[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] Re: Next steps with pv_ops for Xen

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,

If tapdisk dies whilst holding a granted page, the page can never be ungranted, so we leak that page.



Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.