Re: [PATCH 3/3] PPC: KVM: Add support for 64bit TCE windows

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

 




On 05.06.14 14:30, Benjamin Herrenschmidt wrote:
On Thu, 2014-06-05 at 13:56 +0200, Alexander Graf wrote:
What if we ask user space to give us a pointer to user space allocated
memory along with the TCE registration? We would still ask user space to
only use the returned fd for TCE modifications, but would have some
nicely swappable memory we can store the TCE entries in.
That isn't going to work terribly well for VFIO :-) But yes, for
emulated devices, we could improve things a bit, including for
the 32-bit TCE tables.

For emulated, the real mode path could walk the page tables and fallback
to virtual mode & get_user if the page isn't present, thus operating
directly on qemu memory TCE tables instead of the current pinned stuff.

However that has a cost in performance, but since that's really only
used for emulated devices and PAPR VIOs, it might not be a huge issue.

But for VFIO we don't have much choice, we need to create something the
HW can access.

But we need to create separate tables for VFIO anyways, because these TCE tables contain virtual addresses, no?


Alex


In fact, the code as is today can allocate an arbitrary amount of pinned
kernel memory from within user space without any checks.
Right. We should at least account it in the locked limit.

Cheers,
Ben.



--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux