From: Yuichiro NAITO Subject: Re: iavf: panic on QEMU with i440fx chipset emulation To: yasuoka@openbsd.org Cc: kettenis@openbsd.org, tech@openbsd.org Date: Mon, 07 Oct 2024 10:22:00 +0900 From: YASUOKA Masahiko Subject: Re: iavf: panic on QEMU with i440fx chipset emulation Date: Fri, 04 Oct 2024 17:19:28 +0900 (JST) > On Wed, 25 Sep 2024 11:42:02 +0900 (JST) > Yuichiro NAITO wrote: >> Hi, While I'm testing iavf(4) on Linux QEMU with i440fx chipset emulation, >> I had the following panic message on my OpenBSD current build. >> I440fx is the default chipset emulation of QEMU. I know q35 chipset >> emulation is required for msix interrupts. But if users forget to select it, >> I tested what happens on the default chipset emulation. > > I think the root problem is this i440fx situation. No, it's a separate issue. I mean the iavf(4) panic occurs if an error happens between 'iavf_get_vf_resources' and 'if_atatch' in the 'iavf_attach' function. Looking at the 'iavf_attach' function, there are at least 3 functions that may cause an error, 'iavf_config_irq_map', 'pci_intr_map_msix', and 'pci_intr_establish' functions. The 'pci_intr_map_msix' case is 100% reproducible on the QEMU i440fx chipset emulation. The other cases are very rare but should be fixed for stability. > The driver assumes the device works with msix. The physical device is > connected on PCI-E bus and msix is usable of cource. Since QEMU is > doing PCI-passthrough the device to the guest, I think QEMU should > configure a PCI bus which support msxi for the guest. But actually > msix is not usable on OpenBSD guest. > > On FreeBSD, it seems to work around this problem by PCI_QUIRK_ENABLE_MSI_VM > > https://github.com/freebsd/freebsd-src/blob/release/14.1.0/sys/dev/pci/pci.c#L279-L283 > > I think this kind of quirk is needed for us. > What do you think? NetBSD also has the same quirk. https://github.com/NetBSD/src/blob/affb7619d18b17a184eede63a4823f629a2893fc/sys/arch/x86/pci/pci_machdep.c#L273 I agree with you we add the same quirk for OpenBSD. I will send a patch for the PCI bus driver soon. >> ``` >> attempt to execute user address 0x0 in supervisor mode >> kernel: page fault trap, code=10 >> Stopped at 0 TID PID UID PRFLAGS PFLAGS CPU COMMAND >> * 20243 98235 0 0x14000 0x200 0 softnet0 >> locore0.S(0,ffff800000047018,fe00000000079ac2,ffffffffffffffff,ffffffffffffffff,0) at 0 >> taskq_thread(ffff800000047000,ffff800000047000,0,0,ffff800000047000,ffffffff8165acd0) at taskq_thread+0x129 [/usr/src/sys/kern/kern_task.c:451] >> end trace frame: 0x0, count: 14 >> https://www.openbsd.org/ddb.html describes the minimum info required in bug >> reports. Insufficient info makes it difficult to find and fix bugs. >> ddb{0}> >> ``` >> >> It seems that NULL pointer function is called by the 'taskq_thread'. >> Locore0.S is called for the indirect function call to do RETPOLINE >> provided by the '__x86_indirect_thunk_r11' function. >> >> Who sets the NULL pointer function? >> I added the following KASSERT in the 'task_add' function. >> >> ``` >> diff --git a/sys/kern/kern_task.c b/sys/kern/kern_task.c >> index c3dcc5f48cc..d3a2bb90391 100644 >> --- a/sys/kern/kern_task.c >> +++ b/sys/kern/kern_task.c >> @@ -355,6 +355,7 @@ task_add(struct taskq *tq, struct task *w) >> if (ISSET(w->t_flags, TASK_ONQUEUE)) >> return (0); >> >> + KASSERT(w->t_func != NULL); >> mtx_enter(&tq->tq_mtx); >> if (!ISSET(w->t_flags, TASK_ONQUEUE)) { >> rv = 1; >> >> ``` >> >> And then got the following backtrace. >> >> ``` >> panic: kernel diagnostic assertion "w->t_func != NULL" failed: file "/usr/src/sys/kern/kern_task.c", line 358 >> Stopped at db_enter+0x14 [/usr/src/sys/arch/amd64/amd64/db_interface.c:437 >> ]: popq %rbp >> TID PID UID PRFLAGS PFLAGS CPU COMMAND >> * 0 0 0 0x10000 0x200 0K swapper >> db_enter(10,ffffffff83a22770,282,8,ffffffff81425b84,ffffffff83a22770) at db_enter+0x14 [/usr/src/sys/arch/amd64/amd64/db_interface.c:437] >> panic(ffffffff824295f2,ffffffff824295f2,ffff800000046ae0,0,ffff800000135278,ffffffff827a0bee) at panic+0xdd [/usr/src/sys/kern/subr_prf.c:227] >> __assert(ffffffff823dd575,ffffffff82333c7c,166,ffffffff823bd1e5,ffffffff82150ec9,ffffffff83a22830) at __assert+0x29 [/usr/src/sys/kern/subr_prf.c:0] >> task_add(ffff800000047000,ffff800000135278,7e776ef89ea6f47,ffff800000046ae0,fffffd8003a99000,3) at task_add+0xff [/usr/src/sys/kern/kern_task.c:358] >> iavf_process_arq(ffff800000135000,1,70306e848b1765c5,63,ffff800000135000,fffffd8003a97000) at iavf_process_arq+0x451 [/usr/src/sys/dev/pci/if_iavf.c:2260] >> iavf_get_vf_resources(ffff800000135000,ffff800000135000,ae29a6590f97d8d3,ffff8000001355f0,ffff800000135000,ffff800000135600) at iavf_get_vf_resources+0x1cd [/usr/src/sys/dev/pci/if_iavf.c:2543] >> iavf_attach(ffff80000004a200,ffff800000135000,ffffffff83a22a88,ffff80000004a200,58717fcf7319db74,ffff80000004a200) at iavf_attach+0x3d6 [/usr/src/sys/dev/pci/if_iavf.c:850] >> config_attach(ffff80000004a200,ffffffff82784028,ffffffff83a22a88,ffffffff81f8e8 >> f0,19817d1faa76602d,80002000) at config_attach+0x22b [/usr/src/sys/kern/subr_autoconf.c:418] >> pci_probe_device(ffff80000004a200,80002000,0,0,7190d4a2ab338ea0,0) at pci_probe_device+0x595 [/usr/src/sys/dev/pci/pci.c:574] >> pci_enumerate_bus(ffff80000004a200,0,0,ffff80000004a200,4ebe87163eefc827,ffff800000047280) at pci_enumerate_bus+0x1bc [/usr/src/sys/dev/pci/pci.c:0] >> config_attach(ffff800000047280,ffffffff82781cf0,ffffffff83a22ca8,ffffffff81e582b0,19817d1ppfaa6b1255,ffff80000004aa00) at config_attach+0x22b [/usr/src/sys/kern/subr_autoconf.c:418] >> acpipci_attach_bus(ffff800000047280,ffff80000004aa00,8b4a87a3a22af14c,0,ffff800000047280,ffffffff8278c9d8) at acpipci_attach_bus+0x1dd [/usr/src/sys/arch/amd64/pci/acpipci.c:225] >> acpipci_attach_busses(ffff800000047280,ffff800000047280,72b2f1f7da24d7b0,ffffffff83a22dc8,ffff800000047280,ffff800000095980) at acpipci_attach_busses+0x5c [/usr/src/sys/arch/amd64/pci/acpipci.c:233] >> mainbus_attach(0,ffff800000047280,0,0,43135163af729900,0) at mainbus_attach+0x1f3 [/usr/src/sys/arch/amd64/amd64/mainbus.c:253] >> end trace frame: 0xffffffff83a22ee0, count: 0 >> https://www.openbsd.org/ddb.html describes the minimum info required in bug >> reports. Insufficient info makes it difficult to find and fix bugs. >> ddb{0}> >> ``` >> >> From the 'iavf_attach' function, 'iavf_get_vf_resources' is called. >> It expects the response of IAVF_VC_OP_GET_VF_RESOURCES. >> But this backtrace shows 'iavf_process_arq' function is called in the >> 'if_iavf.c:2260' line. It is in the 'iavf_process_vc_event' function. >> >> In my source code, around 'if_iavf.c:2260' is shown as follows. >> >> ``` >> 2231 static void >> 2232 iavf_process_vc_event(struct iavf_softc *sc, struct iavf_aq_desc *desc, >> 2233 struct iavf_aq_buf *buf) >> 2234 { >> 2235 struct iavf_vc_pf_event *event; >> 2236 struct ifnet *ifp = &sc->sc_ac.ac_if; >> 2237 const struct iavf_link_speed *speed; >> 2238 int link; >> 2239 >> 2240 event = buf->aqb_data; >> 2241 switch (event->event) { >> 2242 case IAVF_VC_EVENT_LINK_CHANGE: >> 2243 sc->sc_media_status = IFM_AVALID; >> 2244 sc->sc_media_active = IFM_ETHER; >> 2245 link = LINK_STATE_DOWN; >> 2246 if (event->link_status) { >> 2247 link = LINK_STATE_UP; >> 2248 sc->sc_media_status |= IFM_ACTIVE; >> 2249 >> 2250 ifp->if_baudrate = 0; >> 2251 speed = iavf_find_link_speed(sc, event->link_speed); >> 2252 if (speed != NULL) { >> 2253 sc->sc_media_active |= speed->media; >> 2254 ifp->if_baudrate = speed->baudrate; >> 2255 } >> 2256 } >> 2257 >> 2258 if (ifp->if_link_state != link) { >> 2259 ifp->if_link_state = link; >> 2260 if_link_state_change(ifp); >> 2261 } >> 2262 break; >> ``` >> >> It means that while waiting for IAVF_VC_OP_GET_VF_RESOURCES, >> IAVF_VC_OP_EVENT is returned and then changes the interface media status >> and reports it to userland via the 'if_link_state_change' function. >> >> In the 'if_link_state_change' function, '&ifp->if_linkstatetask' is >> passed to the 'task_add' function. The 'ifp' is a pointer to 'sturct ifnet' >> and the structure entity is in the driver context. So the 'if_linkstatetask' >> is zero cleared at first, and then set by the 'if_attach' function. >> >> Let's back to what the 'iavf_attach' function does. The key points are: >> >> 1. 'iavf_get_vf_resources' triggers 'if_link_state_change' function call. >> 2. 'pci_intr_map_msix' will fail with i440fx because no msix support. >> 3. 'if_attach' won't be called in case of i440fx. >> >> So, the 'if_linkstatetask' is executed with a zero cleared function pointer. >> With the q35 chipset emulation, 'pci_intr_map_msix' succeeds, and >> 'if_attach' is called before executing the 'if_linkstatetask'. >> >> Notifying the link state change is not needed before calling the >> 'if_attach' function because users won't see the interface. >> I added the 'sc_if_attached' flag and changed it to call >> 'if_link_state_change' if the flag is set. See my patch as follows. >> >> I confirmed the kernel doesn't panic and the iavf interfaces won't be >> created with i440fx chipset emulation. >> >> OK? >> >> ``` >> diff --git a/sys/dev/pci/if_iavf.c b/sys/dev/pci/if_iavf.c >> index d573d6725f4..1dd6188bda2 100644 >> --- a/sys/dev/pci/if_iavf.c >> +++ b/sys/dev/pci/if_iavf.c >> @@ -578,6 +578,7 @@ struct iavf_softc { >> uint32_t sc_major_ver; >> uint32_t sc_minor_ver; >> >> + int sc_if_attached; >> int sc_got_vf_resources; >> int sc_got_irq_map; >> uint32_t sc_vf_id; >> @@ -906,6 +907,7 @@ iavf_attach(struct device *parent, struct device *self, void *aux) >> >> if_attach_queues(ifp, iavf_nqueues(sc)); >> if_attach_iqueues(ifp, iavf_nqueues(sc)); >> + sc->sc_if_attached++; >> >> iavf_intr_enable(sc); >> >> @@ -2257,7 +2259,8 @@ iavf_process_vc_event(struct iavf_softc *sc, struct iavf_aq_desc *desc, >> >> if (ifp->if_link_state != link) { >> ifp->if_link_state = link; >> - if_link_state_change(ifp); >> + if (sc->sc_if_attached) >> + if_link_state_change(ifp); >> } >> break; >> >> ``` >> >> -- >> Yuichiro NAITO (naito.yuichiro@gmail.com) >> >> -- Yuichiro NAITO (naito.yuichiro@gmail.com)