Messages in this thread | | | Date | Thu, 7 May 2020 17:59:08 -0400 | From | Peter Xu <> | Subject | Re: [PATCH v2 0/3] vfio-pci: Block user access to disabled device MMIO |
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On Tue, May 05, 2020 at 03:54:36PM -0600, Alex Williamson wrote: > v2: > > Locking in 3/ is substantially changed to avoid the retry scenario > within the fault handler, therefore a caller who does not allow retry > will no longer receive a SIGBUS on contention. IOMMU invalidations > are still not included here, I expect that will be a future follow-on > change as we're not fundamentally changing that issue in this series. > The 'add to vma list only on fault' behavior is also still included > here, per the discussion I think it's still a valid approach and has > some advantages, particularly in a VM scenario where we potentially > defer the mapping until the MMIO BAR is actually DMA mapped into the > VM address space (or the guest driver actually accesses the device > if that DMA mapping is eliminated at some point). Further discussion > and review appreciated. Thanks,
Hi, Alex,
I have a general question on the series.
IIUC this series tries to protect illegal vfio userspace writes to device MMIO regions which may cause platform-level issues. That makes perfect sense to me. However what if the write comes from the devices' side? E.g.:
- Device A maps MMIO region X
- Device B do VFIO_IOMMU_DMA_MAP on Device A's MMIO region X (so X's MMIO PFNs are mapped in device B's IOMMU page table)
- Device A clears PCI_COMMAND_MEMORY (reset, etc.) - this should zap all existing vmas that mapping region X, however device B's IOMMU page table is not aware of this?
- Device B writes to MMIO region X of device A even if PCI_COMMAND_MEMORY cleared on device A's PCI_COMMAND register
Could this happen?
Thanks,
-- Peter Xu
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