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When such a range is encountered during dax_hmem > probe, schedule deferred work and wait for the CXL stack to complete > enumeration and region assembly before deciding ownership. > > Evaluate ownership of Soft Reserved ranges based on CXL region > containment. > > - If all Soft Reserved ranges are fully contained within committed CXL > regions, DROP handling Soft Reserved ranges from dax_hmem and allow > dax_cxl to bind. > > - If any Soft Reserved range is not fully claimed by committed CXL > region, REGISTER the Soft Reserved ranges with dax_hmem. > > Use dax_cxl_mode to coordinate ownership decisions for Soft Reserved > ranges. Once, ownership resolution is complete, flush the deferred work > from dax_cxl before allowing dax_cxl to bind. > > This enforces a strict ownership. Either CXL fully claims the Soft > reserved ranges or it relinquishes it entirely. As I said before, I do not understand why this an all or none decision. If I understood this right, we are not trusting on how the platform is dealing with CXL configuration leading to some soft reserved ranges not having a cxl region. If we do not trust it, why to give such a memory to the kernel through hmem? IMO, it is important to state here the reason for this decision. If I understood this wrongly, I guess it is even more important to explain the reason behind the decision in the commit and maybe as a comment in the code as well. I could not understand it, but at least there would be an explanation. Moreover, as I also commented previously, with Type2 devices, it is almost certain the modules containing the related drivers will not be probed at this point, or if not fully certain, it is a potential possibility. That implies not all the soft reserved regions could have linked cxl regions ... leading to given all those soft reserved ranges to hmem. I know the "approved" solution is Type2 should go without soft reserved memory, but some Type2 devices/drivers could be happy enough with dax. If we do not want to deal with this problem now, at least there should be some indication of this problem. > > Co-developed-by: Dan Williams > Signed-off-by: Dan Williams > Signed-off-by: Smita Koralahalli > --- > drivers/dax/bus.c | 3 ++ > drivers/dax/bus.h | 19 ++++++++++ > drivers/dax/cxl.c | 1 + > drivers/dax/hmem/hmem.c | 78 +++++++++++++++++++++++++++++++++++++++-- > 4 files changed, 99 insertions(+), 2 deletions(-) > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c > index 92b88952ede1..81985bcc70f9 100644 > --- a/drivers/dax/bus.c > +++ b/drivers/dax/bus.c > @@ -25,6 +25,9 @@ DECLARE_RWSEM(dax_region_rwsem); > */ > DECLARE_RWSEM(dax_dev_rwsem); > > +enum dax_cxl_mode dax_cxl_mode = DAX_CXL_MODE_DEFER; > +EXPORT_SYMBOL_NS_GPL(dax_cxl_mode, "CXL"); > + > static DEFINE_MUTEX(dax_hmem_lock); > static dax_hmem_deferred_fn hmem_deferred_fn; > static void *dax_hmem_data; > diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h > index b58a88e8089c..82616ff52fd1 100644 > --- a/drivers/dax/bus.h > +++ b/drivers/dax/bus.h > @@ -41,6 +41,25 @@ struct dax_device_driver { > void (*remove)(struct dev_dax *dev); > }; > > +/* > + * enum dax_cxl_mode - State machine to determine ownership for CXL > + * tagged Soft Reserved memory ranges. > + * @DAX_CXL_MODE_DEFER: Ownership resolution pending. Set while waiting > + * for CXL enumeration and region assembly to complete. > + * @DAX_CXL_MODE_REGISTER: CXL regions do not fully cover Soft Reserved > + * ranges. Fall back to registering those ranges via dax_hmem. > + * @DAX_CXL_MODE_DROP: All Soft Reserved ranges intersecting CXL windows > + * are fully contained within committed CXL regions. Drop HMEM handling > + * and allow dax_cxl to bind. > + */ > +enum dax_cxl_mode { > + DAX_CXL_MODE_DEFER, > + DAX_CXL_MODE_REGISTER, > + DAX_CXL_MODE_DROP, > +}; > + > +extern enum dax_cxl_mode dax_cxl_mode; > + > typedef void (*dax_hmem_deferred_fn)(void *data); > > int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data); > diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c > index a2136adfa186..3ab39b77843d 100644 > --- a/drivers/dax/cxl.c > +++ b/drivers/dax/cxl.c > @@ -44,6 +44,7 @@ static struct cxl_driver cxl_dax_region_driver = { > > static void cxl_dax_region_driver_register(struct work_struct *work) > { > + dax_hmem_flush_work(); > cxl_driver_register(&cxl_dax_region_driver); > } > > diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c > index 1e3424358490..85854e25254b 100644 > --- a/drivers/dax/hmem/hmem.c > +++ b/drivers/dax/hmem/hmem.c > @@ -3,6 +3,7 @@ > #include > #include > #include > +#include > #include "../bus.h" > > static bool region_idle; > @@ -69,8 +70,18 @@ static int hmem_register_device(struct device *host, int target_nid, > if (IS_ENABLED(CONFIG_DEV_DAX_CXL) && > region_intersects(res->start, resource_size(res), IORESOURCE_MEM, > IORES_DESC_CXL) != REGION_DISJOINT) { > - dev_dbg(host, "deferring range to CXL: %pr\n", res); > - return 0; > + switch (dax_cxl_mode) { > + case DAX_CXL_MODE_DEFER: > + dev_dbg(host, "deferring range to CXL: %pr\n", res); > + dax_hmem_queue_work(); > + return 0; > + case DAX_CXL_MODE_REGISTER: > + dev_dbg(host, "registering CXL range: %pr\n", res); > + break; > + case DAX_CXL_MODE_DROP: > + dev_dbg(host, "dropping CXL range: %pr\n", res); > + return 0; > + } > } > > rc = region_intersects_soft_reserve(res->start, resource_size(res)); > @@ -123,8 +134,70 @@ static int hmem_register_device(struct device *host, int target_nid, > return rc; > } > > +static int hmem_register_cxl_device(struct device *host, int target_nid, > + const struct resource *res) > +{ > + if (region_intersects(res->start, resource_size(res), IORESOURCE_MEM, > + IORES_DESC_CXL) != REGION_DISJOINT) > + return hmem_register_device(host, target_nid, res); > + > + return 0; > +} > + > +static int soft_reserve_has_cxl_match(struct device *host, int target_nid, > + const struct resource *res) > +{ > + if (region_intersects(res->start, resource_size(res), IORESOURCE_MEM, > + IORES_DESC_CXL) != REGION_DISJOINT) { > + if (!cxl_region_contains_soft_reserve((struct resource *)res)) > + return 1; > + } > + > + return 0; > +} > + > +static void process_defer_work(void *data) > +{ > + struct platform_device *pdev = data; > + int rc; > + > + /* relies on cxl_acpi and cxl_pci having had a chance to load */ > + wait_for_device_probe(); > + > + rc = walk_hmem_resources(&pdev->dev, soft_reserve_has_cxl_match); > + > + if (!rc) { > + dax_cxl_mode = DAX_CXL_MODE_DROP; > + dev_dbg(&pdev->dev, "All Soft Reserved ranges claimed by CXL\n"); > + } else { > + dax_cxl_mode = DAX_CXL_MODE_REGISTER; > + dev_warn(&pdev->dev, > + "Soft Reserved not fully contained in CXL; using HMEM\n"); > + } > + > + walk_hmem_resources(&pdev->dev, hmem_register_cxl_device); > +} > + > +static void kill_defer_work(void *data) > +{ > + struct platform_device *pdev = data; > + > + dax_hmem_flush_work(); > + dax_hmem_unregister_work(process_defer_work, pdev); > +} > + > static int dax_hmem_platform_probe(struct platform_device *pdev) > { > + int rc; > + > + rc = dax_hmem_register_work(process_defer_work, pdev); > + if (rc) > + return rc; > + > + rc = devm_add_action_or_reset(&pdev->dev, kill_defer_work, pdev); > + if (rc) > + return rc; > + > return walk_hmem_resources(&pdev->dev, hmem_register_device); > } > > @@ -174,3 +247,4 @@ MODULE_ALIAS("platform:hmem_platform*"); > MODULE_DESCRIPTION("HMEM DAX: direct access to 'specific purpose' memory"); > MODULE_LICENSE("GPL v2"); > MODULE_AUTHOR("Intel Corporation"); > +MODULE_IMPORT_NS("CXL");