On Sat, Sep 05, 2026 at 02:29:24PM +0200, Daniel Paziyski wrote: > There are two ways of creating virtual functions: by using the sriov-pf device > parameter (this way, creating a user created VF and binding it to a PF), or > by using a device specific parameter, where the device manually creates a > given > amount of VFs. > > When a PCI device is realized, the device specific realize function is called > first, and then the pcie_sriov_register_device function is called, which > checks > whether the device that has been created is a user created VF, and if it is > the > case and the device allows this kind of VFs, it inserts it into a hashmap, > with > the key being the ID of the PF, and the items being arrays of VFs. > > User created VFs are instantiated independently, and later, when the PF calls > pcie_sriov_pf_init_from_user_created_vfs, it discovers its VFs from the > hashmap > mentioned previously, and sets up in their PCIDevice.ex.sriov_pf structure > the pointer to the PF. This means that, during realization, VFs have no access > to the PF. > > Device created VFs are instantiated during or after PF realization using the > pcie_sriov_pf_init function, which sets up for the VFs the pointer to the PF > before their realization, so when they're realized, they can access the PF > with no issues. > > The problem here is that pcie_sriov_register_device is called after the > realization, and not before. This means that when a user created VF is created > for a device which does not support user created VFs, but supports device > created VFs, the realize function will notice that a VF is being created, and > may try to access the PF, causing a null pointer dereference fault. > > Fix this by placing the user created VF check and registering before the > realization. This way, incorrectly created user created VFs will be noticed, > and device creation will be aborted. > > Additionally, remove from the pcie_sriov_register_device function the top > check. It seems that this check is done to error out if the PF failed for some > reason to initialize its list of user created VFs. However, in such > situations, > the pcie_sriov_pf_init_from_user_created_vfs function will error during > realization, and it will be caught before the check is done at all. Moreover, > since now pcie_sriov_register_device is called before realization, the check > will always fail for PFs with user created VFs, because the list will be > populated during realization. > > The rest of the function though, correctly errors out if a user created VF > is created for an unsupported device type, if a VF is created for a non-PCIe > device, or if the PF is already instantiated, with now the advantage being > that the check is done before the VF instantiation. > > Moreover, move the unregistering of a device's acpi-index and the removal > of a VF from its PF list from pci_qdev_unrealize to do_pci_unregister_device. > We do the former so that the acpi-index is unclaimed on user created VF > creation error, and the latter to not have extra code on the device specific > realization error path. > > When instantiating a user created VF for a NVME controller: > > Command line: > > qemu-system-x86_64 -device nvme-subsys,id=subsys0 \ > -device nvme,id=vctrl0,sriov-pf=ctrl0,subsys=subsys0 \ > -device nvme,id=ctrl0,subsys=subsys0,serial=s > > ASAN splat: > > ../hw/nvme/ctrl.c:9613:28: runtime error: member access within null pointer > of type 'struct NvmeCtrl' > AddressSanitizer:DEADLYSIGNAL > ================================================================= > ==91050==ERROR: AddressSanitizer: SEGV on unknown address 0x000000001cf0 (pc > 0x7f79a8573dcd bp 0x7ffd622c1bc0 sp 0x7ffd622c1b68 T0) > ==91050==The signal is caused by a READ memory access. > #0 0x7f79a8573dcd (/usr/lib/libc.so.6+0x173dcd) (BuildId: > 1fa174a830cef40a5b2388add4318ee2795f573e) > #1 0x5644c6c0266e in nvme_realize ../hw/nvme/ctrl.c:9613 > #2 0x5644c6c67213 in pci_qdev_realize ../hw/pci/pci.c:2316 > #3 0x5644c7a2cfc1 in device_set_realized ../hw/core/qdev.c:514 > #4 0x5644c7a4f767 in property_set_bool ../qom/object.c:2484 > #5 0x5644c7a48d0b in object_property_set ../qom/object.c:1548 > #6 0x5644c7a568a5 in object_property_set_qobject ../qom/qom-qobject.c:28 > #7 0x5644c7a49385 in object_property_set_bool ../qom/object.c:1618 > #8 0x5644c7a2aeb0 in qdev_realize ../hw/core/qdev.c:277 > #9 0x5644c735f29f in qdev_device_add_from_qdict > ../system/qdev-monitor.c:740 > #10 0x5644c735f3ab in qdev_device_add ../system/qdev-monitor.c:758 > #11 0x5644c72b1901 in device_init_func ../system/vl.c:1217 > #12 0x5644c829d4a3 in qemu_opts_foreach ../util/qemu-option.c:1148 > #13 0x5644c72bc33e in qemu_create_cli_devices ../system/vl.c:2762 > #14 0x5644c72bcaa1 in qmp_x_exit_preconfig ../system/vl.c:2822 > #15 0x5644c72c3241 in qemu_init ../system/vl.c:3862 > #16 0x5644c801abf8 in main ../system/main.c:71 > #17 0x7f79a8427780 (/usr/lib/libc.so.6+0x27780) (BuildId: > 1fa174a830cef40a5b2388add4318ee2795f573e) > #18 0x7f79a84278b8 in __libc_start_main (/usr/lib/libc.so.6+0x278b8) > (BuildId: 1fa174a830cef40a5b2388add4318ee2795f573e) > #19 0x5644c5f0a1f4 in _start (BuildId: > 8483f952216d9e345c3744300d0aefa38feb50d7) > > ==91050==Register values: > rax = 0x00007e49988640f0 rbx = 0x00007e49988640f0 rcx = 0x00000fc9b3104828 > rdx = 0x0000000000000058 > rdi = 0x00007e49988640f0 rsi = 0x0000000000001cf0 rbp = 0x00007ffd622c1bc0 > rsp = 0x00007ffd622c1b68 > r8 = 0x00000fc9b3104829 r9 = 0x00000fc9b3104828 r10 = 0x00000fc9b310481e > r11 = 0x00000fc9b310481e > r12 = 0x0000000000001cf0 r13 = 0x00000f6f32e78578 r14 = 0x00000000ffffffff > r15 = 0x00007ffd622c1c10 > AddressSanitizer can not provide additional info. > SUMMARY: AddressSanitizer: SEGV (/usr/lib/libc.so.6+0x173dcd) (BuildId: > 1fa174a830cef40a5b2388add4318ee2795f573e) > ==91050==ABORTING > > Cc: [email protected] > Fixes: 19e55471d4e8 ("pcie_sriov: Allow user to create SR-IOV device") > Signed-off-by: Daniel Paziyski <[email protected]>
/scm/qemu/build/qemu-system-x86_64 -nodefaults -machine q35 -device e1000e,addr=0.0 -device e1000e,addr=0.0 crashes with this: - With the patch: SIGSEGV (exit 139), backtrace at hw/pci/pci.c:2334 in pci_qdev_realize. - Without the patch: exit 1: PCI: slot 0 function 0 not available for e1000e, in use by mch,id=(null). > --- > > This patch is the same as > https://lore.kernel.org/qemu-devel/[email protected]/ > , which improves the original patch by releasing the acpi-index on failure, as > pointed out by Michael S. Tsirkin <[email protected]> on the replies of > https://lore.kernel.org/qemu-devel/[email protected]/ > ("[PATCH 3/3] pcie_sriov: register user created virtual function before > realizing it") > posted on the series > https://lore.kernel.org/qemu-devel/[email protected]/ > ("[PATCH 0/3] NVMe hotunplug and PCI SR-IOV fixes"). > > I am sending this as a patch separate from the series, since imo it was a > mistake > for me to mix unrelated patches on the same series. > > hw/pci/pci.c | 42 ++++++++++++++++++++++++------------------ > hw/pci/pcie_sriov.c | 6 ------ > 2 files changed, 24 insertions(+), 24 deletions(-) > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c > index c15f2b9f08..06c432292f 100644 > --- a/hw/pci/pci.c > +++ b/hw/pci/pci.c > @@ -1223,6 +1223,19 @@ static void pci_config_free(PCIDevice *pci_dev) > g_free(pci_dev->used); > } > > +static void pci_unregister_acpi_index(PCIDevice *pci_dev) > +{ > + if (pci_dev->acpi_index) { > + GSequence *used_indexes = pci_acpi_index_list(); > + > + g_sequence_remove(g_sequence_lookup(used_indexes, > + GINT_TO_POINTER(pci_dev->acpi_index), > + g_cmp_uint32, NULL)); > + > + pci_dev->acpi_index = 0; > + } > +} > + > static void do_pci_unregister_device(PCIDevice *pci_dev) > { > pci_get_bus(pci_dev)->devices[pci_dev->devfn] = NULL; > @@ -1236,6 +1249,9 @@ static void do_pci_unregister_device(PCIDevice *pci_dev) > &pci_dev->bus_master_enable_region); > } > address_space_destroy(&pci_dev->bus_master_as); > + > + pcie_sriov_unregister_device(pci_dev); > + pci_unregister_acpi_index(pci_dev); > } > > /* Extract PCIReqIDCache into BDF format */ > @@ -1487,7 +1503,6 @@ static void pci_qdev_unrealize(DeviceState *dev) > > pci_unregister_io_regions(pci_dev); > pci_del_option_rom(pci_dev); > - pcie_sriov_unregister_device(pci_dev); > > if (pc->exit) { > pc->exit(pci_dev); > @@ -1497,17 +1512,6 @@ static void pci_qdev_unrealize(DeviceState *dev) > do_pci_unregister_device(pci_dev); > > pci_dev->msi_trigger = NULL; > - > - /* > - * clean up acpi-index so it could reused by another device > - */ > - if (pci_dev->acpi_index) { > - GSequence *used_indexes = pci_acpi_index_list(); > - > - g_sequence_remove(g_sequence_lookup(used_indexes, > - GINT_TO_POINTER(pci_dev->acpi_index), > - g_cmp_uint32, NULL)); > - } > } > > void pci_register_bar(PCIDevice *pci_dev, int region_num, > @@ -2318,8 +2322,15 @@ static void pci_qdev_realize(DeviceState *qdev, Error > **errp) > pci_dev = do_pci_register_device(pci_dev, > object_get_typename(OBJECT(qdev)), > pci_dev->devfn, errp); > - if (pci_dev == NULL) > + if (pci_dev == NULL) { > + pci_unregister_acpi_index(pci_dev); So this passes NULL to pci_unregister_acpi_index. > return; > + } > + > + if (!pcie_sriov_register_device(pci_dev, errp)) { > + do_pci_unregister_device(pci_dev); > + return; > + } > > if (pc->realize) { > pc->realize(pci_dev, &local_err); > @@ -2330,11 +2341,6 @@ static void pci_qdev_realize(DeviceState *qdev, Error > **errp) > } > } > > - if (!pcie_sriov_register_device(pci_dev, errp)) { > - pci_qdev_unrealize(DEVICE(pci_dev)); > - return; > - } > - > /* > * A PCIe Downstream Port that do not have ARI Forwarding enabled must > * associate only Device 0 with the device attached to the bus > diff --git a/hw/pci/pcie_sriov.c b/hw/pci/pcie_sriov.c > index c41ac95bee..69930c7b8c 100644 > --- a/hw/pci/pcie_sriov.c > +++ b/hw/pci/pcie_sriov.c > @@ -357,12 +357,6 @@ int16_t > pcie_sriov_pf_init_from_user_created_vfs(PCIDevice *dev, > > bool pcie_sriov_register_device(PCIDevice *dev, Error **errp) > { > - if (!dev->exp.sriov_pf.vf && dev->qdev.id && > - pfs && g_hash_table_contains(pfs, dev->qdev.id)) { > - error_setg(errp, "attaching user-created SR-IOV VF unsupported"); > - return false; > - } > - > if (dev->sriov_pf) { > PCIDevice *pci_pf; > GPtrArray *pf; > -- > 2.55.0
