On 06/25/2014 10:00 AM, Marc Zyngier wrote:
On 25/06/14 15:56, Joel Schopp wrote:
On 06/24/2014 05:28 PM, Peter Maydell wrote:
On 24 June 2014 20:28, Joel Schopp <joel.schopp@xxxxxxx> wrote:
On 06/19/2014 04:21 AM, Marc Zyngier wrote:
The GIC CPU interface is always 4k aligned. If the host is using
64k pages, it is critical to place the guest's GICC interface at the
same relative alignment as the host's GICV. Failure to do so results
in an impossibility for the guest to deal with interrupts.
Add a KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET attribute for the VGIC, allowing
userspace to retrieve the GICV offset in a page. It becomes then trivial
to adjust the GICC base address for the guest.
Does this mean there is a corresponding patch for qemu?
Not as far as I know. It's a bit awkward on the QEMU end because
we really want to provide the guest a consistent memory map
regardless of the host CPU. So at best we'd probably use it to
say "sorry, can't run on this CPU/host kernel".
I think most arm64 servers are going to run with 64k pages. It seems
like a major problem to have qemu not work on these systems.
How many of them will be with the GICC *not* 64kB aligned?
If I'm reading the Server Base System Architecture v2.2 Appendix F
correctly all of them. Here's the relevant quote: "In a 64KB
translation granule system this means that GICC needs to have its base
at 4KB below a 64KB boundary."
(That said, if you think you can make QEMU usefully use the
information and want to write a QEMU patch I'm not averse
to the idea.)
I'll have to think about this approach some more, but I'm not opposed to
doing the work if I thought it was the right thing to do.
kvmtool is probably better placed to take advantage of it since
it takes more of a "deal with what the host provides you"
philosophy.
kvmtool is fun as a play toy, but in the real world nobody is building
clouds using kvmtool, they use kvm with qemu.
A play toy? Hmmm. Do you realise that most of KVM on arm64 has been
written using this play toy?
I meant no insult. I really like kvmtool. I'm just saying that the
eventual end users of these systems will want to run qemu and not kvmtool.
--
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
