Re: [Xen-devel] [PATCH 0/4] x86/IOMMU: multi-vector MSI prerequisites

[suravee suthikulpanit <suravee.suthikulpanit@xxxxxxx>]

On 04/11/2013 02:13 AM, Jan Beulich wrote:
> > > > On 11.04.13 at 03:51, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> 
> > > > wrote:
> > - From drivers/passthrough/amd/iommu_init.c: enable_iommu(), the
> > enabling code tries to set MSI affinity for IOMMU.
> > - From xen/arch/x86/msi.c: set_msi_affinity(), the code tries to
> > "read_msi_msg()" which eventually calls "amd_iommu_read_msi_from_ire()".
> > - Please note that the "amd_iommu_read_msi_from_ire()" was originally
> > empty prior the patch.
> > - From the patch, the new code try to call "get_intremap_entry()", which
> > is the function that was asserting due to table is NULL.
> But even before the patch update_intremap_entry_from_msi_msg()
> also necessarily called get_intremap_entry() for the IOMMU device
> itself. And the respective write_msi_msg() call follows right after the
> read_msi_msg() one, i.e. there's no room for other setup to be done
> by that point. Plus the assertion was there already.
>
> > Here, the MSI read message was sent to read IOMMU registers.  Since the
> > message is targeting for IOMMU itself (bdf 0x2 in this case), it should
> > not be remapped.  That is why I believe the interrupt remapping table is
> > empty.
> Whether or not the MSI for the IOMMU device itself needs to be
> remapped is an independent question, but judging from the
> current code as well as from the specification not saying otherwise
> it needs to be. Confirmation on this would surely be appreciated
> (because otherwise (a) I'd need to understand how this special
> case works with the code before the patch and (b) new special
> casing may need to be added).
>
> In any case - I think I said this before already - seeing a full log up
> to the crash with "iommu=debug" in place might help. After all the
> ACPI tables ought to mention the IOMMU PCI device in some way,
> and hence there ought to be an IVRS mapping as well as an
> associated intremap table. Or else the only way this can work
> currently would be by way of find_iommu_for_device() returning
> NULL for the IOMMU PCI device (which would mean a similar check
> would need to be added to amd_iommu_read_msi_from_ire(), but
> it would then be bogus for the failure there to cause a log message
> to be issued if iommu_debug - that should be trivial to verify on
> an unpatched or older [say 4.2.x based] hypervisor passing
> "iommu=debug").
>
> Jan
I have attached the xl dmesg output from the machine which run the 
non-patched Xen (w/ iommu=debug). It is showing that there is no IVHD 
entry setting up for the bdf 0x2 (the IOMMU).  Also, there is a line 
"AMD-Vi: Fail to find iommu for MSI device id = 0x2) which can be traced 
to xen/drivers/passthrough/amd/iommu_intr.c: 
amd_iommu_msi_msg_update_ire() which is called from xen/arch/x86/msi.c: 
write_msi_msg().
When comparing with other AMD systems in the past (i.e. with SR56XX 
chipset), the IVHD contains IVHD entries such as below:
(XEN) AMD-Vi: IVHD Device Entry: type 0x3 id 0 flags 0
(XEN) AMD-Vi:  Dev_Id Range: 0 -> 0x2

which will generate the mapping entry for bfd 0x0, 0x1, 0x2.

Suravee
PS: I could not get the serial console out from the trouble target 
system (Trinity based), so I could not get the crash message.  But from 
the prior email I sent to first report the issue, you can see that it 
failed during "enable_iommu".

Attachment: tn.xldmesg
Description: tn.xldmesg

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