Re: [PATCH v2 0/5] Address translation for HDM decoding

[Gregory Price <gourry@gourry.net>]

On Mon, Jul 01, 2024 at 07:47:48PM +0200, Robert Richter wrote:
> Default expectation of Linux is that HPA == SPA, which means that
> hardware addresses in the decoders are the same as the kernel sees
> them. However, there are platforms where this is not the case and an
> address translation between decoder's (HPA) and the system's physical
> addresses (SPA) is needed.
> 
> This series implements address translation for HDM decoding. The
> implementation follows the rule that the representation of hardware
> address ranges in the kernel are all SPA. If decoder registers (HDM
> decoder cap or register range) are not SPA, a base offset must be
> applied. Translation happens when accessing the registers back and
> forth. After a read access an address will be converted to SPA and
> before a write access the programmed address is translated from an
> SPA. The decoder register access can be easily encapsulated by address
> translation and thus there are only a few places where translation is
> needed and the code must be changed. This is implemented in patch #2,
> patch #1 is a prerequisite.
> 
> Address translation is restricted to platforms that need it. As such a
> platform check is needed and a flag is introduced for this (patch #3).
> 
> For address translation the base offset must be determined for the
> memory domain. Depending on the platform there are various options for
> this. The address range in the CEDT's CFWMS entry of the CXL host
> bridge can be used to determine the decoder's base address (patch
> #4). This is enabled for AMD Zen4 platforms (patch #5).
> 

Just testing this out, and I'm seeing an inability to actually map the
memory, though the reason escapes me.

Do you have the expected workflow of this down?

For example this fails:

echo ram > /sys/bus/cxl/devices/decoder2.0/mode
echo 0x40000000 > /sys/bus/cxl/devices/decoder2.0/dpa_size
echo region0 > /sys/bus/cxl/devices/decoder0.0/create_ram_region
echo 4096 > /sys/bus/cxl/devices/region0/interleave_granularity
echo 1 > /sys/bus/cxl/devices/region0/interleave_ways
echo 0x40000000 > /sys/bus/cxl/devices/region0/size
echo decoder2.0 > /sys/bus/cxl/devices/region0/target0
^^^^ at this point: -bash: echo: write error: Invalid argument

echo 1 > /sys/bus/cxl/devices/region0/commit

and while the cxl driver sees the correct topology, the current version
of cxl-cli reports the memdevs as "anonymous" and reports a failure to
lookup the targets for a region

without adding too much bulk to the email

[~/ndctl]# ./build/cxl/cxl list -vvvvv
libcxl: cxl_mappings_init: region0 target0:  lookup failure
[
  {
    "anon memdevs":[
      {
        "memdev":"mem0",
        "ram_size":137438953472,
...
      {
        "memdev":"mem1",
        "ram_size":137438953472,
...
  {
    "buses":[
      {
...
        "decoders:root0":[
          {
            "decoder":"decoder0.0",
            "resource":825975898112,
            "size":260382392320,
            "interleave_ways":1,
            "max_available_extent":260382392320,
            "volatile_capable":true,
            "qos_class":1,
            "nr_targets":1,
            "targets":[
              {
                "target":"pci0000:00",
                "alias":"ACPI0016:01",
                "position":0,
                "id":0
              }
            ],
            "regions:decoder0.0":[
              {
                "region":"region0",
                "resource":825975898112,
                "size":260382392320,
                "type":"ram",
                "interleave_ways":1,
                "interleave_granularity":256,
                "decode_state":"reset",
                "state":"disabled",
                "mappings":[
                ]
              }
...

Do you have a sense of what might generate this behavior?

~Gregory

> Changelog:
> 
> v2:
>  * Fixed build error for other archs [kbot]
> 
> 
> Robert Richter (5):
>   cxl/hdm: Moving HDM specific code to core/hdm.c.
>   cxl/hdm: Implement address translation for HDM decoding
>   cxl/acpi: Add platform flag for HPA address translation
>   cxl/hdm: Setup HPA base for address translation using the HPA window
>     in CFMWS
>   cxl/acpi: Enable address translation for Zen4 platforms
> 
>  drivers/cxl/acpi.c      |  16 +++
>  drivers/cxl/core/core.h |   2 +
>  drivers/cxl/core/hdm.c  | 245 ++++++++++++++++++++++++++++++++++++++--
>  drivers/cxl/core/pci.c  | 119 +------------------
>  drivers/cxl/cxl.h       |   2 +
>  drivers/cxl/cxlmem.h    |   4 +
>  drivers/cxl/cxlpci.h    |   3 -
>  7 files changed, 262 insertions(+), 129 deletions(-)
> 
> 
> base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
> -- 
> 2.39.2
>