Re: [Xen-devel] [PATCH v3 0/4] x86/iommu: PVH Dom0 workarounds for missing RMRR entries

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Wed, Aug 8, 2018 at 3:54 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 08.08.18 at 10:25, <roger.pau@xxxxxxxxxx> wrote:
> > On Tue, Aug 07, 2018 at 10:45:32AM -0600, Tamas K Lengyel wrote:
> >> On Tue, Aug 7, 2018 at 10:04 AM Tamas K Lengyel
> >> <tamas.k.lengyel@xxxxxxxxx> wrote:
> >> (XEN) [VT-D]iommu.c:919: iommu_fault_status: Fault Overflow
> >> (XEN) [VT-D]iommu.c:921: iommu_fault_status: Primary Pending Fault
> >> (XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
> >> 428f926000, iommu reg = ffff82c000a0c000
> >> (XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
> >> (XEN) print_vtd_entries: iommu #0 dev 0000:00:02.0 gmfn 428f926
> >> (XEN)     root_entry[00] = 43aaae001
> >> (XEN)     context[10] = 2_43cf92001
> >> (XEN)     l4[000] = 9c0000043cf91107
> >> (XEN)     l3[10a] = 8000000000000000
> >> (XEN)     l3[10a] not present
> >>
> >> The fault is repeated a million times per second and the system is
> >> pretty much stalled.
> >
> > As Jan says, this page is outside of any range in the memory map. I
> > wonder however what's in there.
> >
> > I think (also seeing the PV issues) you should bring this up with the
> > driver maintainers, it might actually be a bug that the driver is
> > trying to access such address.
>
> Right, especially considering that the address does not appear to be
> invariant, I suspect the driver sets up some I/O from (presumably)
> uninitialized data. This goes unnoticed until DMA translation comes
> into play. Tamas - did you try enabling DMA translation in Linux
> when not running on top of Xen? Depending on the
> CONFIG_INTEL_IOMMU_DEFAULT_ON setting this may not be the
> default.

I checked and this kernel option is not enabled. Are you suggesting to
try booting just Linux with this option enabled to see what happens?

>
> > In the meantime, you can try to add to the command line:
> >
> > rmrr=0x428f926=0:0:2.0
> >
> > In order to force an iommu mapping of this address.
>
> I suspect this won't help much.
>

The mfn is not always the same but seems to be at least on some
occasion. I managed to reboot with the right rmrr= option set but I'm
still getting the same faults over and over for that mfn I set in the
rmrr= option.

Tamas

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