lkml.org 
[lkml]   [2016]   [Dec]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: possible dmar_init_reserved_ranges() error
On Mon, Dec 19, 2016 at 03:20:44PM -0600, Bjorn Helgaas wrote:
> Hi guys,
>
> I have some questions about dmar_init_reserved_ranges(). On systems
> where CPU physical address space is not identity-mapped to PCI bus
> address space, e.g., where the PCI host bridge windows have _TRA
> offsets, I'm not sure we're doing the right thing.
>
> Assume we have a PCI host bridge with _TRA that maps CPU addresses
> 0x80000000-0x9fffffff to PCI bus addresses 0x00000000-0x1fffffff, with
> two PCI devices below it:
>
> PCI host bridge domain 0000 [bus 00-3f]
> PCI host bridge window [mem 0x80000000-0x9fffffff] (bus 0x00000000-0x1fffffff]
> 00:00.0: BAR 0 [mem 0x80000000-0x8ffffffff] (0x00000000-0x0fffffff on bus)
> 00:01.0: BAR 0 [mem 0x90000000-0x9ffffffff] (0x10000000-0x1fffffff on bus)
>
> The IOMMU init code in dmar_init_reserved_ranges() reserves the PCI
> MMIO space for all devices:
>
> pci_iommu_init()
> intel_iommu_init()
> dmar_init_reserved_ranges()
> reserve_iova(0x80000000-0x8ffffffff)
> reserve_iova(0x90000000-0x9ffffffff)
>
> This looks odd because we're reserving CPU physical addresses, but
> the IOVA space contains *PCI bus* addresses. On most x86 systems they
> would be the same, but not on all.

While we're looking at this, here's another question. We do basically
this:

dmar_init_reserved_ranges()
{
...
for_each_pci_dev(pdev) {
for (i = 0; i < PCI_NUM_RESOURCES; i++) {
r = &pdev->resource[i];
reserve_iova(r)

But I assume it's possible to have more than one IOTLB in a system,
so you could have some PCI devices under one IOTLB and others under a
different IOTLB. So it seems like we should reserve only the IOVA
space used by the devices under *this* IOTLB.

Also, we may hot-add a device under the IOTLB, and I don't see where
we reserve the IOVA space it uses.

I think the best thing to do would be to reserve the host bridge
apertures related to each IOTLB. That would resolve both questions.
It looks like iova_reserve_pci_windows() does this in the
iommu_dma_init_domain() path.

Bjorn

\
 
 \ /
  Last update: 2016-12-28 00:45    [W:0.132 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site