Re: [PATCH v6 0/5] Handling of multiple PCI

Ojeda Leon, Nicolas <ncoleon@...>

On Wed, 22 Jun 2022 at 17:35, Ard Biesheuvel <ardb@...> wrote:

On Tue, 21 Jun 2022 at 23:28, Nicolas Ojeda Leon <ncoleon@...> wrote:

Increased control is provided in Ovmf platforms to define and
configure the specifications of multiple PCI host bridges in the
hypervisor. The host propagates this information to the guest,
initially through fw-cfg interface.

In some AWS EC2 platforms, we expose a PCI topology including
several root bridges portraying information about physical
distribution that enables the guest to optimize accesses. Current
PCI driver for Ovmf enables the explicit definition of multiple root
bridges and contains the logic to fix their resources based on
platform-specific PCD entries. However, we need a way to control,
from the hypervisor, how many and which resources each PCI root
bridge can use. For this reason, this patch series introduces a
mechanism to provide PCI host bridges information like bus number
range, attributes, allocation attributes, PIO aperture as well as 32
and 64- bit prefetchable and non-prefetchable MMIO ranges through a
fw-cfg item created by the hypervisor and consumed by the guest
firmware. In order to offer a generic and extensible way to disclose
non-discoverable hardware information from the host to the guest, a
new library called HardwareInfoLib is created in the OvmfPkg. In
essence, this library offers the functionality to parse a generic
BLOB into a list as well as the methods to iterate over such list, including filtering options.
The library is conceived in a generic way so that further hardware
elements can also be described using it. For such purpose the length
of the BLOB is not restricted but instead regarded as a sequence of
header-info elements that allow the parsing during runtime.
Furthermore, specific functionality is provided wrapping
QemuFwCfgReadBytes to extract hardware descriptions, in the
aforementioned format, in a static way so that early in the Pei
stage the library can be used to identify address space requirements.
The core of the library offers enough flexibility to process as many
elements, even from different hardware types (heterogenous), as
needed in a single run. This library is extended for the particular
use case already exposed, PCI host bridges, and this same code
offers an example of how to tailor it for further hardware components.

After acknowledgement from Gerd Hoffmann and fixing all warnings and
errors found by the CI pipeline (via draft pull request), here I
send a new revision of the patches for merging.

Prepearation for upstream merge:
- No functional change at all.
- Small changes to fix all builds excercised by CI
- Added libraries to furhter platforms as per dependencies requirements
- Explicit casting of some values as required by build and
verification of values when demoting values.
- Arranged added files copyright to the format required.
- Changed HOST_BRIDGE_INFO bitfield member to UINT32 to follow
EDK2 guidelines motivated on build in 32-bit windows systems.
- Added verification of Bus Number range when values provided by
host to make sure Root Bridge is initialized with valid values

- Removed last 3 patches dealing with pre-populated resources to
encapsulate related changes in more manageable chunks and while
pre-populated changes are finalized.
- Added Acked-by to all commits
- Re-based on top of latest master and refactored changes in
MemDetect.c to adapt to recently created

- Minor modification to use MAX_UINT64 as global invalid base address
when reading PCI host bridge information provided by the host
(Patch 1)
- Refactor PciHostBridgeUtilityGetRootBridges into a thin wrapper that
calls 2 new function: one (BusScan) that performs the legacy bus
scan population process and a new one (HostProvided) that populates
Root Bridges with host provided values. (Patch 5)
- Move code that sets value of PcdPciPreservePopulatedMappings token
based on host-provided fw-cfg file into the function that populates
root bridges with host provided data (Patch 6)
- Restructured base address retrieval to leave PCI Resource Allocation
protocol untouched and instead augment the existing services to
enable base address retrieval before allocation. (Patch 7)
- Use new method to retrieve Root Bridge base addresses before
allocation and use that to handle pre-populated BARs (Patch 8)

Nicolas Ojeda Leon (5):
OvmfPkg/Library: Create base HardwareInfoLib for PCI Host Bridges
Ovmf/HardwareInfoLib: Create Pei lib to parse directly from fw-cfg
Ovmf/HardwareInfoLib: Add Dxe lib to dynamically parse heterogenous
Ovmf/PlatformPei: Use host-provided GPA end if available
OvmfPkg/PciHostBridgeUtilityLib: Initialize RootBridges apertures with
Merged as #3000,

Thanks all,
This series appears to have triggered a failure in our CI. Could someone propose a fix please?
Thanks Ard for notifying.

I will post the fix in short, tested build locally and now running the CI pipeline (

Best regards,


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