29.10.2025 14:01, Jonathan Cameron via пишет:
On Tue, 28 Oct 2025 22:26:12 +0300
Michael Tokarev <[email protected]> wrote:
On 10/6/25 20:08, Michael Tokarev wrote:
On 10/5/25 22:17, Michael S. Tsirkin wrote:
From: peng guo <[email protected]>
When using a CXL Type 3 device together with a virtio 9p device in
QEMU on a
physical server, the 9p device fails to initialize properly. The
kernel reports
the following error:
virtio: device uses modern interface but does not have
VIRTIO_F_VERSION_1
9pnet_virtio virtio0: probe with driver 9pnet_virtio failed with
error -22
Further investigation revealed that the 64-bit BAR space assigned to
the 9pnet
device was overlapped by the memory window allocated for the CXL
devices. As a
result, the kernel could not correctly access the BAR region, causing the
virtio device to malfunction.
An excerpt from /proc/iomem shows:
480010000-cffffffff : CXL Window 0
480010000-4bfffffff : PCI Bus 0000:00
4c0000000-4c01fffff : PCI Bus 0000:0c
4c0000000-4c01fffff : PCI Bus 0000:0d
4c0200000-cffffffff : PCI Bus 0000:00
4c0200000-4c0203fff : 0000:00:03.0
4c0200000-4c0203fff : virtio-pci-modern
To address this issue, this patch adds the reserved memory end
calculation
for cxl devices to reserve sufficient address space and ensure that
CXL memory
windows are allocated beyond all PCI 64-bit BARs. This prevents
overlap with
64-bit BARs regions such as those used by virtio or other pcie devices,
resolving the conflict.
QEMU Build Configuration:
./configure --prefix=/home/work/qemu_master/build/ \
--target-list=x86_64-softmmu \
--enable-kvm \
--enable-virtfs
QEMU Boot Command:
sudo /home/work/qemu_master/qemu/build/qemu-system-x86_64 \
-nographic -machine q35,cxl=on -enable-kvm -m 16G -smp 8 \
-hda /home/work/gp_qemu/rootfs.img \
-virtfs local,path=/home/work/gp_qemu/
share,mount_tag=host0,security_model=passthrough,id=host0 \
-kernel /home/work/linux_output/arch/x86/boot/bzImage \
--append "console=ttyS0 crashkernel=256M root=/dev/sda
rootfstype=ext4 rw loglevel=8" \
-object memory-backend-ram,id=vmem0,share=on,size=4096M \
-device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
-device cxl-
rp,port=0,bus=cxl.1,id=root_port13,chassis=0,slot=2 \
-device cxl-type3,bus=root_port13,volatile-
memdev=vmem0,id=cxl-vmem0,sn=0x123456789 \
-M cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G
Fixes: 03b39fcf64bc ("hw/cxl: Make the CXL fixed memory window setup a
machine parameter")
Signed-off-by: peng guo <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
---
hw/i386/pc.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
Hi!
Is it qemu-stable material (10.0.x & 10.1.x)?
I think it does make sense for stable.
Aha. I remember now why I had this question to begin with.
If it should be applied to 10.0.x series too (which is an LTS series),
I need help back-porting it before commit 8b1c560937467d0d9
"hw/i386/pc: Remove PCMachineClass::broken_reserved_end field"
which touches the same code.
If it's worth the effort to begin with.
Meanwhile I picked it up for 10.1.x.
Thank you!
/mjt
