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)? > > A friendly ping for the stable series? I think it does make sense for stable. Thanks, Jonathan > > Thanks, > > /mjt >
