Re: [PATCH V2 4/4] intel-iommu: PASID support

[Jason Wang]

On Sat, Apr 2, 2022 at 3:24 PM Tian, Kevin <kevin.tian@intel.com> wrote:
>
> > From: Jason Wang <jasowang@redhat.com>
> > Sent: Wednesday, March 30, 2022 4:32 PM
> >
> > On Wed, Mar 30, 2022 at 4:02 PM Tian, Kevin <kevin.tian@intel.com> wrote:
> > >
> > > > From: Jason Wang <jasowang@redhat.com>
> > > > Sent: Tuesday, March 29, 2022 12:49 PM
> > > >
> > > > On Mon, Mar 28, 2022 at 3:03 PM Tian, Kevin <kevin.tian@intel.com>
> > wrote:
> > > > >
> > > > > > From: Jason Wang
> > > > > > Sent: Monday, March 21, 2022 1:54 PM
> > > > > >
> > > > > > +    /*
> > > > > > +     * vtd-spec v3.4 3.14:
> > > > > > +     *
> > > > > > +     * """
> > > > > > +     * Requests-with-PASID with input address in range 0xFEEx_xxxx
> > are
> > > > > > +     * translated normally like any other request-with-PASID 
> > > > > > through
> > > > > > +     * DMA-remapping hardware. However, if such a request is
> > processed
> > > > > > +     * using pass-through translation, it will be blocked as 
> > > > > > described
> > > > > > +     * in the paragraph below.
> > > > >
> > > > > While PASID+PT is blocked as described in the below paragraph, the
> > > > > paragraph itself applies to all situations:
> > > > >
> > > > >   1) PT + noPASID
> > > > >   2) translation + noPASID
> > > > >   3) PT + PASID
> > > > >   4) translation + PASID
> > > > >
> > > > > because...
> > > > >
> > > > > > +     *
> > > > > > +     * Software must not program paging-structure entries to remap
> > any
> > > > > > +     * address to the interrupt address range. Untranslated 
> > > > > > requests
> > > > > > +     * and translation requests that result in an address in the
> > > > > > +     * interrupt range will be blocked with condition code LGN.4 or
> > > > > > +     * SGN.8.
> > > > >
> > > > > ... if you look at the definition of LGN.4 or SGN.8:
> > > > >
> > > > > LGN.4:  When legacy mode (RTADDR_REG.TTM=00b) is enabled,
> > hardware
> > > > >         detected an output address (i.e. address after remapping) in 
> > > > > the
> > > > >         interrupt address range (0xFEEx_xxxx). For Translated 
> > > > > requests and
> > > > >         requests with pass-through translation type (TT=10), the 
> > > > > output
> > > > >         address is the same as the address in the request
> > > > >
> > > > > The last sentence in the first paragraph above just highlights the 
> > > > > fact
> > that
> > > > > when input address of PT is in interrupt range then it is blocked by
> > LGN.4
> > > > > or SGN.8 due to output address also in interrupt range.
> > > > >
> > > > > > +     * """
> > > > > > +     *
> > > > > > +     * We enable per as memory region (iommu_ir_fault) for catching
> > > > > > +     * the tranlsation for interrupt range through PASID + PT.
> > > > > > +     */
> > > > > > +    if (pt && as->pasid != PCI_NO_PASID) {
> > > > > > +        memory_region_set_enabled(&as->iommu_ir_fault, true);
> > > > > > +    } else {
> > > > > > +        memory_region_set_enabled(&as->iommu_ir_fault, false);
> > > > > > +    }
> > > > > > +
> > > > >
> > > > > Given above this should be a bug fix for nopasid first and then apply 
> > > > > it
> > > > > to pasid path too.
> > > >
> > > > Actually, nopasid path patches were posted here.
> > > >
> > > > https://www.mail-archive.com/qemu-
> > devel@nongnu.org/msg867878.html
> > > >
> > > > Thanks
> > > >
> > >
> > > Can you elaborate why they are handled differently?
> >
> > It's because that patch is for the case where pasid mode is not
> > implemented. We might need it for -stable.
> >
>
> So will that patch be replaced after this one goes in?

That path will be merged first if I understand correctly. Then this
patch could be applied on top.

> By any means
> the new iommu_ir_fault region could be applied to both nopasid
> and pasid i.e. no need toggle it when address space is switched.

Actually it's needed only when PT is enabled. When PT is disabled, the
translation is done via iommu_translate.

Considering the previous patch will be merged, I will fix this !PT in
the next version.

Thanks

>
> Thanks
> Kevin