Re: [PATCH v4 11/14] cxl/atl: Lock decoders that need address translation

Robert Richter
2025-11-13T20:05:12Z

On 12.11.25 09:34:34, Dave Jiang wrote:
>
>
> On 11/11/25 5:54 AM, Robert Richter wrote:
> > On 04.11.25 10:13:34, Dave Jiang wrote:
> >>
> >>
> >> On 11/3/25 11:47 AM, Robert Richter wrote:
> >>> There is only support to translate addresses from an endpoint to its
> >>> CXL host bridge, but not in the opposite direction from the bridge to
> >>> the endpoint. Thus, the endpoint address range cannot be determined
> >>> and setup manually for a given SPA range of a region. If the endpoint
> >>> has address translation enabled, lock it to prevent the kernel from
> >>> reconfiguring it.
> >>>
> >>> Reviewed-by: Gregory Price <gourry@gourry.net>
> >>> Signed-off-by: Robert Richter <rrichter@amd.com>
> >>> ---
> >>> drivers/cxl/core/atl.c | 10 ++++++++++
> >>> 1 file changed, 10 insertions(+)
> >>>
> >>> diff --git a/drivers/cxl/core/atl.c b/drivers/cxl/core/atl.c
> >>> index d6aa7e6d0ac5..5c15e4d12193 100644
> >>> --- a/drivers/cxl/core/atl.c
> >>> +++ b/drivers/cxl/core/atl.c
> >>> @@ -158,6 +158,16 @@ static int cxl_prm_translate_hpa_range(struct cxl_root *cxl_root, void *data)
> >>> return -ENXIO;
> >>> }
> >>>
> >>> + /*
> >>> + * There is only support to translate from the endpoint to its
> >>> + * parent port, but not in the opposite direction from the
> >>> + * parent to the endpoint. Thus, the endpoint address range
> >>> + * cannot be determined and setup manually. If the address range
> >>> + * was translated and modified, forbid reprogramming of the
> >>> + * decoders and lock them.
> >>> + */
> >>> + cxld->flags |= CXL_DECODER_F_LOCK;
> >>
> >
> >> Feels like this should be something the BIOS should enforce if that
> >> is the expectation? And the kernel checks and warns if that is not
> >> the case.
> >
> > I think this is more a limitation of the kernel implementation rather
> > than the BIOS. The BIOS provides enought information by CFMWS, PRM,
> > HDM and PCI topology. In theory and if there is demand for it, support
> > could be added for driver region setup.
>

> But shouldn't the BIOS set the decoder lock rather than the kernel
> setting a software lock flag based on assumption of the PRM based
> setup?

If BIOS locks the decoders, it cannot be removed even for the case
there the OS can actually handle it.

-Robert