Re: [PATCH 1/2] Revert "xen: Disable PCI on qemuarm with Xen"

Bertrand Marquis

Hi Michal,

On 9 Jun 2022, at 10:57, Michal Orzel via <> wrote:

This reverts commit fb0a7b97db4f419b82309f98a4944ae3330d1e2e.

Commit fb0a7b97db4f removed the PCI node from the qemu device tree
due to the issue when trying to access PCI configuration space that
was causing Linux running on top of Xen to end up in an infinite loop.
The investigation showed that the problem occurs due to qemu placing
ECAM space at 256GiB mark. Even though Xen officially supports on arm32
up to 12GiB of physical address space, it is able to map it correctly
for dom0. However, when Linux tries to access the ECAM space and the
stage2 translation fault occurs, HPFAR register contains incorrect IPA.
We can say it is incorrect because using hardware AT instruction or
software lookup, we can obtain the correct IPA from the same VA. This
can suggest that the problem is related to QEMU fault handling.

Instead of removing the PCI node the follow-up commit will disable
highmem option in qemu which will cause placing ECAM space in the
32-bit space.

Signed-off-by: Michal Orzel <michal.orzel@...>
Reviewed-by: Bertrand Marquis <bertrand.marquis@...>

Also tested on kirkstone and dom0 boots fine and pci is working.

Thanks a lot

classes/qemuboot-xen-dtb.bbclass | 22 ----------------------
1 file changed, 22 deletions(-)

diff --git a/classes/qemuboot-xen-dtb.bbclass b/classes/qemuboot-xen-dtb.bbclass
index 1f17a86..d43d23a 100644
--- a/classes/qemuboot-xen-dtb.bbclass
+++ b/classes/qemuboot-xen-dtb.bbclass
@@ -63,21 +63,6 @@ write_lops_xen_section() {

-write_lop_rm_pci() {
- cat <<EOF >"$1"
-/ {
- compatible = "system-device-tree-v1";
- lops {
- lop_1 {
- compatible = "system-device-tree-v1,lop,modify";
- modify = "/pcie@10000000::";
- };
- };
write_lop_add_to_xen_cmdline() {
cat <<EOF >"$1"
@@ -150,13 +135,6 @@ generate_xen_qemuboot_dtb() {
write_lop_add_to_xen_cmdline "${B}/lop-xen-cmdline.dts" \

- # On Qemu Arm32, Dom0 accessing PCI config space ends up in an
- # infinite loop. Remove pci node from the device tree
- if [ "${MACHINE}" = "qemuarm" ]; then
- write_lop_rm_pci "${B}/lop-rm-pci.dts"
- LOP_MODULE_ARGS="${LOP_MODULE_ARGS} -i ${B}/lop-rm-pci.dts"
- fi
if [ -z "${QB_XEN_DOMAIN_MODULES}" ]; then
bbwarn "No domain modules: please set QB_XEN_DOMAIN_MODULES"

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