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Re: [PATCH v1 2/6] xen/arm: Reserve resources for virtio-pci



Hi Edgar,

On 24/09/2024 17:23, Edgar E. Iglesias wrote:
From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>

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.iglesias@xxxxxxx>
---
  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.

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?

Cheers,

--
Julien Grall




 


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