On Fri, Oct 31, 2025 at 10:13:15AM +0000, Jonathan Cameron wrote: > On Wed, 29 Oct 2025 17:10:55 +0300 > Michael Tokarev <[email protected]> wrote: > > > 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. > > I don't have strong opinions either way. peng guo, if you happen > to be in a position to backport and test with QEMU LTS that would be > great. > > Jonathan Hi Jonathan,
I'll move forward with back-porting and testing with the QEMU LTS as soon as possible. Apologies for the delayed reply. I didn't have a computer and env before because i was on vacation. BR Peng. > > > > > If it's worth the effort to begin with. > > > > Meanwhile I picked it up for 10.1.x. > > > > Thank you! > > > > /mjt
