[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v6 1/3] x86/msi: harden stale pdev handling
On Mon, Oct 28, 2024 at 05:58:28PM +0100, Jan Beulich wrote: > On 18.10.2024 22:39, Stewart Hildebrand wrote: > > Dom0 normally informs Xen of PCI device removal via > > PHYSDEVOP_pci_device_remove, e.g. in response to SR-IOV disable or > > hot-unplug. We might find ourselves with stale pdevs if a buggy dom0 > > fails to report removal via PHYSDEVOP_pci_device_remove. In this case, > > attempts to access the config space of the stale pdevs would be invalid > > and return all 1s. > > > > Some possible conditions leading to this are: > > > > 1. Dom0 disables SR-IOV without reporting VF removal to Xen. > > > > The Linux SR-IOV subsystem normally reports VF removal when a PF driver > > disables SR-IOV. In case of a buggy dom0 SR-IOV subsystem, SR-IOV could > > become disabled with stale dangling VF pdevs in both dom0 Linux and Xen. > > > > 2. Dom0 reporting PF removal without reporting VF removal. > > > > During SR-IOV PF removal (hot-unplug), a buggy PF driver may fail to > > disable SR-IOV, thus failing to remove the VFs, leaving stale dangling > > VFs behind in both Xen and Linux. At least Linux warns in this case: > > > > [ 100.000000] 0000:01:00.0: driver left SR-IOV enabled after remove > > > > In either case, Xen is left with stale VF pdevs, risking invalid PCI > > config space accesses. > > > > When Xen is built with CONFIG_DEBUG=y, the following Xen crashes were > > observed when dom0 attempted to access the config space of a stale VF: > > > > (XEN) Assertion 'pos' failed at arch/x86/msi.c:1274 > > (XEN) ----[ Xen-4.20-unstable x86_64 debug=y Tainted: C ]---- > > ... > > (XEN) Xen call trace: > > (XEN) [<ffff82d040346834>] R pci_msi_conf_write_intercept+0xa2/0x1de > > (XEN) [<ffff82d04035d6b4>] F pci_conf_write_intercept+0x68/0x78 > > (XEN) [<ffff82d0403264e5>] F > > arch/x86/pv/emul-priv-op.c#pci_cfg_ok+0xa0/0x114 > > (XEN) [<ffff82d04032660e>] F > > arch/x86/pv/emul-priv-op.c#guest_io_write+0xb5/0x1c8 > > (XEN) [<ffff82d0403267bb>] F > > arch/x86/pv/emul-priv-op.c#write_io+0x9a/0xe0 > > (XEN) [<ffff82d04037c77a>] F x86_emulate+0x100e5/0x25f1e > > (XEN) [<ffff82d0403941a8>] F x86_emulate_wrapper+0x29/0x64 > > (XEN) [<ffff82d04032802b>] F pv_emulate_privileged_op+0x12e/0x217 > > (XEN) [<ffff82d040369f12>] F do_general_protection+0xc2/0x1b8 > > (XEN) [<ffff82d040201aa7>] F > > x86_64/entry.S#handle_exception_saved+0x2b/0x8c > > > > (XEN) Assertion 'pos' failed at arch/x86/msi.c:1246 > > (XEN) ----[ Xen-4.20-unstable x86_64 debug=y Tainted: C ]---- > > ... > > (XEN) Xen call trace: > > (XEN) [<ffff82d040346b0a>] R pci_reset_msix_state+0x47/0x50 > > (XEN) [<ffff82d040287eec>] F pdev_msix_assign+0x19/0x35 > > (XEN) [<ffff82d040286184>] F > > drivers/passthrough/pci.c#assign_device+0x181/0x471 > > (XEN) [<ffff82d040287c36>] F iommu_do_pci_domctl+0x248/0x2ec > > (XEN) [<ffff82d040284e1f>] F iommu_do_domctl+0x26/0x44 > > (XEN) [<ffff82d0402483b8>] F do_domctl+0x8c1/0x1660 > > (XEN) [<ffff82d04032977e>] F pv_hypercall+0x5ce/0x6af > > (XEN) [<ffff82d0402012d3>] F lstar_enter+0x143/0x150 > > > > These ASSERTs triggered because the MSI-X capability position can't be > > found for a stale pdev. > > > > Latch the capability positions of MSI and MSI-X during device init, and > > replace instances of pci_find_cap_offset(..., PCI_CAP_ID_MSI{,X}) with > > the stored value. Introduce one additional ASSERT, while the two > > existing ASSERTs in question continue to work as intended, even with a > > stale pdev. > > > > Fixes: 484d7c852e4f ("x86/MSI-X: track host and guest mask-all requests > > separately") > > Fixes: 575e18d54d19 ("pci: clear {host/guest}_maskall field on assign") > > Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx> > > Looks largely okay to me now, just two type selection aspects: > > > --- a/xen/arch/x86/msi.c > > +++ b/xen/arch/x86/msi.c > > @@ -278,23 +278,21 @@ void __msi_set_enable(u16 seg, u8 bus, u8 slot, u8 > > func, int pos, int enable) > > > > static void msi_set_enable(struct pci_dev *dev, int enable) > > { > > - int pos; > > + int pos = dev->msi_pos; > > This and ... > > > u16 seg = dev->seg; > > u8 bus = dev->bus; > > u8 slot = PCI_SLOT(dev->devfn); > > u8 func = PCI_FUNC(dev->devfn); > > > > - pos = pci_find_cap_offset(dev->sbdf, PCI_CAP_ID_MSI); > > if ( pos ) > > __msi_set_enable(seg, bus, slot, func, pos, enable); > > } > > > > static void msix_set_enable(struct pci_dev *dev, int enable) > > { > > - int pos; > > + int pos = dev->msix_pos; > > ... this want to become unsigned int at this occasion, imo. Like we have ... > > > @@ -764,7 +762,7 @@ static int msix_capability_init(struct pci_dev *dev, > > u8 slot = PCI_SLOT(dev->devfn); > > u8 func = PCI_FUNC(dev->devfn); > > bool maskall = msix->host_maskall, zap_on_error = false; > > - unsigned int pos = pci_find_cap_offset(dev->sbdf, PCI_CAP_ID_MSIX); > > + unsigned int pos = dev->msix_pos; > > ... e.g. here already. > > > --- a/xen/include/xen/pci.h > > +++ b/xen/include/xen/pci.h > > @@ -113,6 +113,9 @@ struct pci_dev { > > pci_sbdf_t sbdf; > > }; > > > > + unsigned int msi_pos; > > + unsigned int msix_pos; > > + > > uint8_t msi_maxvec; > > uint8_t phantom_stride; > > As can be seen from the subsequent members, we're trying to be space > conserving here. Both fields won't require more than 8 bits, so uint8_t > or unsigned char would be the better type to use. Again imo. Preferably > with those adjustments (which could likely be done while committing) > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> uint8_t would seem preferable here, as it's fixed-size width clearly related to the offset into the PCI configuration space for a device. It might also be worth noting in the commit message that having the position cached should be a small perf improvement, by not having to walk the capability list each time. Anyway, no strong opinion about the commit message adjustment, so with the type changed: Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> Thanks, Roger.
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