> -----Original Message----- > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > Sent: Saturday, November 15, 2014 7:23 AM > To: Bjorn Helgaas > Cc: Allan, Bruce W; linux-pci@xxxxxxxxxxxxxxx; iommu@lists.linux- > foundation.org > Subject: Re: DMA_ALIAS_DEVFN issue > > On Fri, 2014-11-14 at 21:25 -0700, Bjorn Helgaas wrote: > > [+cc Alex, add a subject] > > > > On Fri, Nov 14, 2014 at 6:49 PM, Allan, Bruce W <bruce.w.allan@xxxxxxxxx> > wrote: > > > Let's try this again as plain text... > > > > > > For a PCIe device with SR-IOV support enabled (e.g. the PF device ID > > is 0xf001 at 0000:07:00.0 and the 16 VFs have device ID 0xf002 at > > 0000:07:01.0 through 0000:07:02.7), if the hardware attempts a DMA > > read/write of memory that was mapped by the PF devfn but instead uses > > a requester id of one of the VF devfns (enabled but not yet assigned > > to a VM) it fails and generates log messages similar to: > > > > > > [ 416.800881] dmar: DRHD: handling fault status reg 2 > > > [ 416.800887] dmar: DMAR:[DMA Read] Request device [07:02.2] fault > addr ffff0000 > > > DMAR:[fault reason 02] Present bit in context entry is clear > > This is exactly what IOMMU isolation is meant to do. A buffer mapped > for one device should not be accessible from another device. It really > doesn't matter if the devices are related as VF/PF, VF/VF, or PF/PF. > > > > Shouldn't a DMA alias quirk that sets the > > PCI_DEV_FLAGS_DMA_ALIAS_DEVFN flag and dma_alias_devfn to the PF > devfn > > for all VF devfns work-around this issue, or am I misunderstanding > > what a DMA alias quirk is supposed to do? If a DMA alias quirk cannot > > resolve this, what is the most appropriate way to handle this? > > The buffer needs to be mapped for each VF. If for some reason the VF > needs implicit access to a PF mapped buffer then this devices is > completely broken from an isolation perspective and using DMA aliases to > fix it means that individual VFs will never be assignable to guests. > Thanks, > > Alex Hmm, that...is unfortunate. Thanks Alex for the clarification, and thanks Bjorn for adding Alex and a proper subject to the thread. Bruce. ��.n��������+%������w��{.n�����{���"�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
