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Re: [Xen-devel] [RFC PATCH 3/3] tools, libxl: handle the iomem parameter with the memory_mapping hcall

Hello Arianna,

Adding Ian Jackson, maintainer of libxl.

On 02/03/14 08:49, Arianna Avanzini wrote:
Currently, the configuration-parsing code concerning the handling of the
iomem parameter only invokes the XEN_DOMCTL_iomem_permission hypercall.
This commit lets the XEN_DOMCTL_memory_mapping hypercall be invoked
after XEN_DOMCTL_iomem_permission when the iomem parameter is parsed
from a domU configuration file.

Do you plan to give I/O mem range which is not describe by the device tree?

IHMO, allow the user to specify which I/O mem region will be mapped to the guest on ARM is wrong. As the platform is described via the device tree, the guest configuration should have a list of node to map to domU. Then {lib,}xl will parse/map/update the DT node to the guest.

Signed-off-by: Arianna Avanzini <avanzini.arianna@xxxxxxxxx>
Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Cc: Paolo Valente <paolo.valente@xxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Eric Trudeau <etrudeau@xxxxxxxxxxxx>
Cc: Viktor Kleinik <viktor.kleinik@xxxxxxxxxxxxxxx>
  tools/libxl/libxl_create.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index a604cd8..7da0778 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -1099,6 +1099,16 @@ static void domcreate_launch_dm(libxl__egc *egc, 
libxl__multidev *multidev,
                   "failed give dom%d access to iomem range %"PRIx64"-%"PRIx64,
                   domid, io->start, io->start + io->number - 1);
              ret = ERROR_FAIL;
+        } else {
+            ret = xc_domain_memory_mapping(CTX->xch, domid,
+                                           io->start, io->start,
+                                           io->number, 1);
+            if (ret < 0) {
+                LOGE(ERROR,
+                     "failed to map to dom%d iomem range %"PRIx64"-%"PRIx64,
+                     domid, io->start, io->start + io->number - 1);
+                ret = ERROR_FAIL;
+            }

This code is common on both x86 and ARM. On x86, we don't want to map
the I/O mem region in the guest here. QEMU will do it later.

The 1:1 mapping doesn't seem correct because the range could clash with the guest layout (e.g: GIC base address, RAM base address) which is for now hardcoded (see xen/include/public/arch-arm.h:358).

I have various solution to fix this issue:
- Relocate the GIC/RAM base address and notify Xen that the GIC base address has changed. So we can keep the 1:1 mapping.
  - Let libxl decide where to map the I/O mem range in the guest.

For the latter solution, we will have to find a way to tell to the guest : "This I/O mem range is here ...". Perhaps via the device tree.


Julien Grall

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