Hi Edgar,
On 24/09/2024 18:11, Edgar E. Iglesias wrote:
On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote:
Hi Edgar,
On 24/09/2024 17:23, Edgar E. Iglesias wrote:
From: "Edgar E. Iglesias" <edgar.igles...@amd.com>
Reserve memory ranges and interrupt lines for an externally
emulated PCI controller (e.g by QEMU) dedicated to hosting
Virtio devices and potentially other emulated devices.
Signed-off-by: Edgar E. Iglesias <edgar.igles...@amd.com>
---
xen/include/public/arch-arm.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index e19f0251a6..654b827715 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t;
#define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM @ 8GB
*/
#define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000)
+/* Virtio PCI - Ordered by decreasing size to keep things aligned */
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000)
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE xen_mk_ullong(0x0f000000000)
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000)
+
+#define GUEST_VIRTIO_PCI_ECAM_BASE (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \
+ GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE)
+#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000)
+
+#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000)
+#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + \
+ GUEST_VIRTIO_PCI_ECAM_SIZE)
+#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000)
Why is this specific to virtio PCI? However, I am not entirely convinced we
should have a second PCI hostbridge exposed to the guest for a few reasons:
1. This require to reserve yet another range in the address space (could
be solved with a more dynamic layout)
2. From your instructions, the guest needs to explicitly do a PCI rescan.
Another big advantage I forgot to mention is disaggregation. In a world
where the hostbridge is handled in Xen, you could have a PCI device
emulated by dom0 while the other is emulated by a stub domain.
So rather than having a second hostbridge, have you considered to extend the
existing hostbridge (implemented in Xen) to support a mix of physical PCI
device and virtual one?
Thanks Julien,
It's briefly come up in a couple of discussions but I haven't looked
carefully at it. It is a good idea and it's probably worth prototyping
to see what the gaps are in hypercall interfaces, QEMU support etc.
I also vaguely recall to discuss it on xen-devel. But I couldn't find
the discussion... :(.
I think all the hypercalls should be there but will require some
plumbing in Xen on Arm. QEMU should be able to request Xen to forward
configuration access for a given PCI device (see XEN_DMOP_IO_RANGE_PCI).
They will then be forwarded to QEMU using IOREQ_TYPE_PCI_CONFIG.
We also have an hypercall to be able to inject interrupts from QEMU (see
XEN_DMOP_set_irq_level).
Cheers,
--
Julien Grall
