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 > > If it's worth the effort to begin with. > > Meanwhile I picked it up for 10.1.x. > > Thank you! > > /mjt
