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Fri, 18 Jul 2025 21:35:47 +0800 (CST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=buaa.edu.cn; s=buaa; h=Received:From:To:Cc:Subject:Date: Message-ID:MIME-Version:Content-Transfer-Encoding; bh=XPkEBDNisX Q0AjoTAXlD7TIcavVVweP0kvy5/P95cf4=; b=bL8pMsgQ59jFJCYrtuGBG90ChC z68SS5YDe8So53tW/tym8iQpexsao4GDbjghqk5XoVkMO/2biOWppbf6GIxbKjtS MIAjXJjOB+aojGnelYpoDh83JHF0Ddfo4zoBKk5rkZgJ6sd/5iQkSFoR5B7g6zl/ OssH8VH6KvHvxiqjk= To: mst@redhat.com, marcel.apfelbaum@gmail.com, pbonzini@redhat.com, richard.henderson@linaro.org, eduardo@habkost.net, qemu-devel@nongnu.org, linux-cxl@vger.kernel.org Cc: wyguopeng@163.com, peng guo Subject: [PATCH] hw/i386/pc: Avoid overlap between CXL window and PCI 64bit BARs in QEMU Date: Fri, 18 Jul 2025 21:35:45 +0800 Message-ID: <20250718133545.5261-1-engguopeng@buaa.edu.cn> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: Nyz+CgAXM5mzTXpoDL2qBQ--.55176S2 X-Coremail-Antispam: 1UD129KBjvJXoWxXr4xKFW8AF1UXrWrCr1xXwb_yoW5XFW5p3 sxtay5GFWFgr13GFZ7Xas5Ca18uFs5u3W7CFs2gwn29rnxKr15ZasFy3yYv340qrn3Jry7 XF98JrySqw4DuaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvY1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s1l1IIY67AE w4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2 IY67AKxVW7JVWDJwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVW8Jr0_Cr1UM28EF7xvwVC2 z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v26rxl6s0DM2AIxVAIcxkEcV Aq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMcIj6xIIjxv20xvE14v26r10 6r15McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64 vIr41lF7I21c0EjII2zVCS5cI20VAGYxC7MxkIecxEwVAFwVW5GwCF04k20xvY0x0EwIxG rwCF04k20xvE74AGY7Cv6cx26F1DJr1UJwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c 02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_ GFylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7 CjxVAFwI0_Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v2 6r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0J UkHUDUUUUU= X-CM-SenderInfo: d2isijirrujqpexdthxhgxhubq/ Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=20.188.111.126; envelope-from=engguopeng@buaa.edu.cn; helo=azure-sdnproxy.icoremail.net X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-to: peng guo From: peng guo via Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1752845846939116600 Content-Type: text/plain; charset="utf-8" When using a CXL Type 3 device together with a virtio 9p device in QEMU, the 9p device fails to initialize properly. The kernel reports the following: 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 9p= net device was overlapped by the memory window allocated for the CXL devices. A= s 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 uses the value of `cxl_resv_end` to reser= ve 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=20 as those used by virtio or other pcie devices, resolving the conflict. QEMU Build Configuration: ./configure --prefix=3D/home/work/qemu_master/build/ \ --target-list=3Dx86_64-softmmu \ --enable-kvm \ --enable-virtfs QEMU Boot Command: sudo /home/work/qemu_master/qemu/build/qemu-system-x86_64 \ -nographic -machine q35,cxl=3Don -enable-kvm -m 16G -smp 8 \ -hda /home/work/gp_qemu/rootfs.img \ -virtfs local,path=3D/home/work/gp_qemu/share,mount_tag=3Dhost0,sec= urity_model=3Dpassthrough,id=3Dhost0 \ -kernel /home/work/linux_output/arch/x86/boot/bzImage \ --append "console=3DttyS0 crashkernel=3D256M root=3D/dev/sda rootfs= type=3Dext4 rw loglevel=3D8" \ -object memory-backend-ram,id=3Dvmem0,share=3Don,size=3D4096M \ -device pxb-cxl,bus_nr=3D12,bus=3Dpcie.0,id=3Dcxl.1 \ -device cxl-rp,port=3D0,bus=3Dcxl.1,id=3Droot_port13,chassis=3D0,sl= ot=3D2 \ -device cxl-type3,bus=3Droot_port13,volatile-memdev=3Dvmem0,id=3Dcx= l-vmem0,sn=3D0x123456789 \ -M cxl-fmw.0.targets.0=3Dcxl.1,cxl-fmw.0.size=3D4G Tested in a QEMU setup with a CXL Type 3 device and a 9pnet virtio device. Signed-off-by: peng guo --- hw/i386/pc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 2f58e73d3347..180bc615f3f0 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -975,7 +975,7 @@ void pc_memory_init(PCMachineState *pcms, =20 rom_set_fw(fw_cfg); =20 - if (machine->device_memory) { + if (machine->device_memory || cxl_resv_end) { uint64_t *val =3D g_malloc(sizeof(*val)); uint64_t res_mem_end; =20 --=20 2.43.0