Re: [PATCH v3 0/5] ACPI: DMA ranges management

[Feng Kan]

On Wed, Nov 29, 2017 at 11:28 PM, Feng Kan <fkan@xxxxxxx> wrote:
> On Thu, Aug 3, 2017 at 5:32 AM, Lorenzo Pieralisi
> <lorenzo.pieralisi@xxxxxxx> wrote:
>> This patch series is v3 of a previous posting:
>>
>> v2->v3:
>>         - Fixed DMA masks computation
>>         - Fixed size computation overflow in acpi_dma_get_range()
>>
>> v1->v2:
>>         - Reworked acpi_dma_get_range() flow and logs
>>         - Added IORT named component address limits
>>         - Renamed acpi_dev_get_resources() helper function
>>         - Rebased against v4.13-rc3
>>
>> v2: http://lkml.kernel.org/r/20170731152323.32488-1-lorenzo.pieralisi@xxxxxxx
>> v1: http://lkml.kernel.org/r/20170720144517.32529-1-lorenzo.pieralisi@xxxxxxx
>>
>> -- Original cover letter --
>>
>> As reported in:
>>
>> http://lkml.kernel.org/r/CAL85gmA_SSCwM80TKdkZqEe+S1beWzDEvdki1kpkmUTDRmSP7g@xxxxxxxxxxxxxx
>>
>> the bus connecting devices to an IOMMU bus can be smaller in size than
>> the IOMMU input address bits which results in devices DMA HW bugs in
>> particular related to IOVA allocation (ie chopping of higher address
>> bits owing to system bus HW capabilities mismatch with the IOMMU).
>>
>> Fortunately this problem can be solved through an already present but never
>> used ACPI 6.2 firmware bindings (ie _DMA object) allowing to define the DMA
>> window for a specific bus in ACPI and therefore all upstream devices
>> connected to it.
>>
>> This small patch series enables _DMA parsing in ACPI core code and
>> use it in ACPI IORT code in order to detect DMA ranges for devices and
>> update their data structures to make them work with their related DMA
>> addressing restrictions.
>>
>> Cc: Will Deacon <will.deacon@xxxxxxx>
>> Cc: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
>> Cc: Feng Kan <fkan@xxxxxxx>
>> Cc: Jon Masters <jcm@xxxxxxxxxx>
>> Cc: Robert Moore <robert.moore@xxxxxxxxx>
>> Cc: Robin Murphy <robin.murphy@xxxxxxx>
>> Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
>> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
>>
>> Lorenzo Pieralisi (5):
>>   ACPICA: resource_mgr: Allow _DMA method in walk resources
>>   ACPI: Make acpi_dev_get_resources() method agnostic
>>   ACPI: Introduce DMA ranges parsing
>>   ACPI: Make acpi_dma_configure() DMA regions aware
>>   ACPI/IORT: Add IORT named component memory address limits
>>
>>  drivers/acpi/acpica/rsxface.c |  7 ++--
>>  drivers/acpi/arm64/iort.c     | 57 ++++++++++++++++++++++++++-
>>  drivers/acpi/resource.c       | 82 +++++++++++++++++++++++++++++---------
>>  drivers/acpi/scan.c           | 91 +++++++++++++++++++++++++++++++++++++++----
>>  include/acpi/acnames.h        |  1 +
>>  include/acpi/acpi_bus.h       |  2 +
>>  include/linux/acpi.h          |  8 ++++
>>  include/linux/acpi_iort.h     |  5 ++-
>>  8 files changed, 219 insertions(+), 34 deletions(-)
>>
>> --
>> 2.10.0
>>
> Lorenzo:
>
> A network driver can use pci_set_dma_mask or its like to override what
> is done with this patch here.
> Which would result in iova allocation greater than the original _DMA
> aperture. Should we force
> the dma_set_mask to not change if an existing mask is already set?

Let me clarify the question some more, in our system the IOMMU supports only
42 bits of address. With your _DMA aperture patch, the initial dma_mask and
coherent_mask are correctly set by the code. However, the device driver can
set the dma_mask and coherent mask at a later point which over writes the
initial setting by your code. In which case, once the iova is exhausted with the
32 bit address, it will start seeking more iova address via the
dma_limit. In this
case it would fail my system since the iommu.aperture_end is that of 48 bits
as derived from ias field in  the SMMU.

Should the dma_limit be the smallest of driver->dma_mask, iommu.aperture_end and
your _DMA aperture size via ACPI table? Rather than just the
driver->dma_mask and
iommu.aperture_end. This will ensure the smallest/correct aperture is used.