Re: [PATCH RFC 0/7] PCI/HMAT: Describe P2PDMA reachability and performance

On Mon, Aug 24, 2026 at 01:15:34PM -0700, Alison Schofield wrote:
> On Wed, Aug 12, 2026 at 10:47:37PM +0300, Leon Romanovsky wrote:
> > Linux derives P2PDMA reachability from visible PCI topology, ACS
> > configuration, and a host-bridge whitelist. It cannot describe conditional
> > or slower cross-host-bridge paths; passthrough can hide the physical peer
> > relationships.
> > 
> > This RFC series implements the proposed ACPI HMAT Type 3 extension below.
> 
> Hi Leon,
> 
> Is there an ECN document for review alongside this?
> I get that the table below is a snapshot of the expected change, but
> would appreciate the long version to read.

Sure, Mahesh sent me the document, which I promised to convert to the
mailing list format. I will send the official RFC to the linux-acpi ML
slightly later.

Thanks

> 
> Please add linux-cxl to CC list on future postings.
> 
> -- Alison
> 
> 
> > Directional Generic Port matrices describe reachability, ordering, latency,
> > and bandwidth. Linux uses ordered paths to authorize P2PDMA and their
> > latency/bandwidth to rank providers. A VMM could translate these matrices
> > into guest domains; that is outside this series.
> > 
> >   HMAT Type 3 structure
> > 
> >   Field               Offset       Bytes  Meaning
> >   ---------------------------------------------------------------
> >   Type:                    0           2  value 3
> >   Length:                  4           4  entire structure
> >   Flags:                   8           1  traffic classes
> >   Data-type:               9           1  metric selector
> >   Initiators:             12           4  Generic Port count (s)
> >   Targets:                16           4  Generic Port count (t)
> >   Base-unit:              24           8  ps or MB/s; non-zero
> >   Initiator-PDs:          32         4*s  proximity-domain list
> >   Target-PDs:         32+4*s         4*t  proximity-domain list
> >   Matrix:         32+4*(s+t)       2*s*t  directional Entry[i][j]
> >   Reserved: bytes 2-3, 10-11, and 20-23
> > 
> >   Flags: encoding
> >     bit 0  non-UIO
> >     bit 1  UIO
> > 
> >   Metrics: selector
> >     0/1/2  access/read/write latency
> >     3/4/5  access/read/write bandwidth
> > 
> >   Direction: Initiator PD[i] -- Entry[i][j] metric --> Target PD[j]
> > 
> > ----------------------------------------------------------------------
> > Based on [PATCH v3 00/17] PCI/P2PDMA: Fix ACS egress control handling
> > https://lore.kernel.org/all/[email protected]/
> > 
> > Signed-off-by: Leon Romanovsky <[email protected]>
> > ---
> > Leon Romanovsky (7):
> >       ACPICA: Define PCIe P2P latency and bandwidth information
> >       ACPI: HMAT: Make PCIe P2P paths available to consumers
> >       PCI/P2PDMA: Authorize HMAT-described cross-host-bridge P2P
> >       PCI/P2PDMA: Prefer providers with better HMAT performance
> >       ACPI: HMAT: Add KUnit tests for PCIe P2P matrix semantics
> >       PCI/P2PDMA: Add KUnit tests for HMAT policy boundaries
> >       PCI/P2PDMA: Add KUnit tests for HMAT provider ranking
> > 
> >  drivers/acpi/numa/Kconfig     |  13 ++
> >  drivers/acpi/numa/Makefile    |   1 +
> >  drivers/acpi/numa/hmat.c      | 245 +++++++++++++++++++++-
> >  drivers/acpi/numa/hmat_test.c | 223 ++++++++++++++++++++
> >  drivers/acpi/numa/hmat_test.h |  17 ++
> >  drivers/pci/Kconfig           |  14 ++
> >  drivers/pci/Makefile          |   1 +
> >  drivers/pci/p2pdma.c          | 300 ++++++++++++++++++++------
> >  drivers/pci/p2pdma_test.c     | 477 ++++++++++++++++++++++++++++++++++++++++++
> >  drivers/pci/pci.h             |  23 ++
> >  include/acpi/actbl1.h         |  27 ++-
> >  include/linux/acpi.h          |  26 +++
> >  12 files changed, 1298 insertions(+), 69 deletions(-)
> > ---
> > base-commit: bc5261fca94dd94ab557cc0852ce465d9c3ab8b0
> > change-id: 20260715-hmat-p2p-eb4971a9d731
> > 
> > Best regards,
> > --  
> > Leon Romanovsky <[email protected]>
> > 
>