Re: [PATCH 07/26] cxl/port: Add dynamic capacity size support to endpoint decoders

Jonathan Cameron
2024-04-05T13:54:47Z

On Sun, 24 Mar 2024 16:18:10 -0700
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
>
> To support Dynamic Capacity Devices (DCD) endpoint decoders will need to
> map DC partitions (regions). In addition to assigning the size of the
> DC partition, the decoder must assign any skip value from the previous
> decoder. This must be done within a contiguous DPA space.
>
> Two complications arise with Dynamic Capacity regions which did not
> exist with Ram and PMEM partitions. First, gaps in the DPA space can
> exist between and around the DC Regions. Second, the Linux resource
> tree does not allow a resource to be marked across existing nodes within
> a tree.
>
> For clarity, below is an example of an 60GB device with 10GB of RAM,
> 10GB of PMEM and 10GB for each of 2 DC Regions. The desired CXL mapping
> is 5GB of RAM, 5GB of PMEM, and all 10GB of DC1.
>
> DPA RANGE
> (dpa_res)
> 0GB 10GB 20GB 30GB 40GB 50GB 60GB
> |----------|----------|----------|----------|----------|----------|
>
> RAM PMEM DC0 DC1
> (ram_res) (pmem_res) (dc_res[0]) (dc_res[1])
> |----------|----------| <gap> |----------| <gap> |----------|
>
> RAM PMEM DC1
> |XXXXX|----|XXXXX|----|----------|----------|----------|XXXXXXXXXX|
> 0GB 5GB 10GB 15GB 20GB 30GB 40GB 50GB 60GB

To add another corner to the example, maybe map only part of DC1?

>
> The previous skip resource between RAM and PMEM was always a child of
> the RAM resource and fit nicely [see (S) below]. Because of this
> simplicity this skip resource reference was not stored in any CXL state.
> On release the skip range could be calculated based on the endpoint
> decoders stored values.
>
> Now when DC1 is being mapped 4 skip resources must be created as
> children. One for the PMEM resource (A), two of the parent DPA resource
> (B,D), and one more child of the DC0 resource (C).
>
> 0GB 10GB 20GB 30GB 40GB 50GB 60GB
> |----------|----------|----------|----------|----------|----------|
> | |
> |----------|----------| | |----------| | |----------|
> | | | | |
> (S) (A) (B) (C) (D)
> v v v v v
> |XXXXX|----|XXXXX|----|----------|----------|----------|XXXXXXXXXX|
> skip skip skip skip skip
>
> Expand the calculation of DPA freespace and enhance the logic to support
> mapping/unmapping DC DPA space. To track the potential of multiple skip
> resources an xarray is attached to the endpoint decoder. The existing
> algorithm between RAM and PMEM is consolidated within the new one to
> streamline the code even though the result is the storage of a single
> skip resource in the xarray.
>
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes for v1:
> [iweiny: Update cover letter]
> ---
> drivers/cxl/core/hdm.c | 192 +++++++++++++++++++++++++++++++++++++++++++-----
> drivers/cxl/core/port.c | 2 +
> drivers/cxl/cxl.h | 2 +
> 3 files changed, 179 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index e22b6f4f7145..da7d58184490 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -210,6 +210,25 @@ void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds)
> }
> EXPORT_SYMBOL_NS_GPL(cxl_dpa_debug, CXL);
>
> +static void cxl_skip_release(struct cxl_endpoint_decoder *cxled)
> +{
> + struct cxl_dev_state *cxlds = cxled_to_memdev(cxled)->cxlds;
> + struct cxl_port *port = cxled_to_port(cxled);
> + struct device *dev = &port->dev;
> + unsigned long index;
> + void *entry;
> +
> + xa_for_each(&cxled->skip_res, index, entry) {
> + struct resource *res = entry;
> +
> + dev_dbg(dev, "decoder%d.%d: releasing skipped space; %pr\n",
> + port->id, cxled->cxld.id, res);
> + __release_region(&cxlds->dpa_res, res->start,
> + resource_size(res));
> + xa_erase(&cxled->skip_res, index);
> + }
> +}
> +
> /*
> * Must be called in a context that synchronizes against this decoder's
> * port ->remove() callback (like an endpoint decoder sysfs attribute)
> @@ -220,15 +239,11 @@ static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
> struct cxl_port *port = cxled_to_port(cxled);
> struct cxl_dev_state *cxlds = cxlmd->cxlds;
> struct resource *res = cxled->dpa_res;
> - resource_size_t skip_start;
>
> lockdep_assert_held_write(&cxl_dpa_rwsem);
>
> - /* save @skip_start, before @res is released */
> - skip_start = res->start - cxled->skip;
> __release_region(&cxlds->dpa_res, res->start, resource_size(res));
> - if (cxled->skip)
> - __release_region(&cxlds->dpa_res, skip_start, cxled->skip);
> + cxl_skip_release(cxled);
> cxled->skip = 0;
> cxled->dpa_res = NULL;
> put_device(&cxled->cxld.dev);
> @@ -263,6 +278,100 @@ static int dc_mode_to_region_index(enum cxl_decoder_mode mode)
> return mode - CXL_DECODER_DC0;
> }
>
> +static int cxl_request_skip(struct cxl_endpoint_decoder *cxled,
> + resource_size_t skip_base, resource_size_t skip_len)
> +{
> + struct cxl_dev_state *cxlds = cxled_to_memdev(cxled)->cxlds;
> + const char *name = dev_name(&cxled->cxld.dev);
> + struct cxl_port *port = cxled_to_port(cxled);
> + struct resource *dpa_res = &cxlds->dpa_res;
> + struct device *dev = &port->dev;
> + struct resource *res;
> + int rc;
> +
> + res = __request_region(dpa_res, skip_base, skip_len, name, 0);
> + if (!res)
> + return -EBUSY;
> +
> + rc = xa_insert(&cxled->skip_res, skip_base, res, GFP_KERNEL);
> + if (rc) {
> + __release_region(dpa_res, skip_base, skip_len);
> + return rc;
> + }
> +
> + dev_dbg(dev, "decoder%d.%d: skipped space; %pr\n",
> + port->id, cxled->cxld.id, res);
> + return 0;
> +}
> +
> +static int cxl_reserve_dpa_skip(struct cxl_endpoint_decoder *cxled,
> + resource_size_t base, resource_size_t skipped)
> +{
> + struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> + struct cxl_port *port = cxled_to_port(cxled);
> + struct cxl_dev_state *cxlds = cxlmd->cxlds;
> + resource_size_t skip_base = base - skipped;
> + struct device *dev = &port->dev;
> + resource_size_t skip_len = 0;
> + int rc, index;
> +
> + if (resource_size(&cxlds->ram_res) && skip_base <= cxlds->ram_res.end) {
> + skip_len = cxlds->ram_res.end - skip_base + 1;
> + rc = cxl_request_skip(cxled, skip_base, skip_len);
> + if (rc)
> + return rc;
> + skip_base += skip_len;
> + }
> +
> + if (skip_base == base) {
> + dev_dbg(dev, "skip done ram!\n");
> + return 0;
> + }
> +
> + if (resource_size(&cxlds->pmem_res) &&
> + skip_base <= cxlds->pmem_res.end) {
> + skip_len = cxlds->pmem_res.end - skip_base + 1;
> + rc = cxl_request_skip(cxled, skip_base, skip_len);
> + if (rc)
> + return rc;
> + skip_base += skip_len;
> + }
> +
> + index = dc_mode_to_region_index(cxled->mode);
> + for (int i = 0; i <= index; i++) {
> + struct resource *dcr = &cxlds->dc_res[i];
> +
> + if (skip_base < dcr->start) {
> + skip_len = dcr->start - skip_base;
> + rc = cxl_request_skip(cxled, skip_base, skip_len);
> + if (rc)
> + return rc;
> + skip_base += skip_len;
> + }
> +
> + if (skip_base == base) {
> + dev_dbg(dev, "skip done DC region %d!\n", i);
> + break;
> + }
> +
> + if (resource_size(dcr) && skip_base <= dcr->end) {
> + if (skip_base > base) {
> + dev_err(dev, "Skip error DC region %d; skip_base %pa; base %pa\n",
> + i, &skip_base, &base);
> + return -ENXIO;
> + }
> +
> + skip_len = dcr->end - skip_base + 1;
> + rc = cxl_request_skip(cxled, skip_base, skip_len);
> + if (rc)
> + return rc;
> + skip_base += skip_len;
> + }
> + }
> +
> + return 0;
> +}
> +
> static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> resource_size_t base, resource_size_t len,
> resource_size_t skipped)
> @@ -300,13 +409,12 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> }
>
> if (skipped) {
> - res = __request_region(&cxlds->dpa_res, base - skipped, skipped,
> - dev_name(&cxled->cxld.dev), 0);
> - if (!res) {
> - dev_dbg(dev,
> - "decoder%d.%d: failed to reserve skipped space\n",
> - port->id, cxled->cxld.id);
> - return -EBUSY;
> + int rc = cxl_reserve_dpa_skip(cxled, base, skipped);
> +
> + if (rc) {
> + dev_dbg(dev, "decoder%d.%d: failed to reserve skipped space; %pa - %pa\n",
> + port->id, cxled->cxld.id, &base, &skipped);
> + return rc;
> }
> }
> res = __request_region(&cxlds->dpa_res, base, len,
> @@ -314,14 +422,20 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> if (!res) {
> dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
> port->id, cxled->cxld.id);
> - if (skipped)
> - __release_region(&cxlds->dpa_res, base - skipped,
> - skipped);
> + cxl_skip_release(cxled);
> return -EBUSY;
> }
> cxled->dpa_res = res;
> cxled->skip = skipped;
>
> + for (int mode = CXL_DECODER_DC0; mode <= CXL_DECODER_DC7; mode++) {
> + int index = dc_mode_to_region_index(mode);
> +
> + if (resource_contains(&cxlds->dc_res[index], res)) {
> + cxled->mode = mode;
> + goto success;
> + }
> + }
> if (resource_contains(&cxlds->pmem_res, res))
> cxled->mode = CXL_DECODER_PMEM;
> else if (resource_contains(&cxlds->ram_res, res))
> @@ -332,6 +446,9 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> cxled->mode = CXL_DECODER_MIXED;
> }
>
> +success:
> + dev_dbg(dev, "decoder%d.%d: %pr mode: %d\n", port->id, cxled->cxld.id,
> + cxled->dpa_res, cxled->mode);
> port->hdm_end++;
> get_device(&cxled->cxld.dev);
> return 0;
> @@ -463,14 +580,14 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
>
> int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
> {
> + resource_size_t free_ram_start, free_pmem_start, free_dc_start;
> struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> - resource_size_t free_ram_start, free_pmem_start;
> struct cxl_port *port = cxled_to_port(cxled);
> struct cxl_dev_state *cxlds = cxlmd->cxlds;
> struct device *dev = &cxled->cxld.dev;
> resource_size_t start, avail, skip;
> struct resource *p, *last;
> - int rc;
> + int rc, dc_index;
>
> down_write(&cxl_dpa_rwsem);

Obviously not related to this patch as such, but maybe a good place
for scoped_guard() to avoid the dance around unlocking the rwsem
and allow some early returns on the error paths.

> if (cxled->cxld.region) {
> @@ -500,6 +617,21 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
> else
> free_pmem_start = cxlds->pmem_res.start;
>
> + /*
> + * Limit each decoder to a single DC region to map memory with
> + * different DSMAS entry.
> + */
> + dc_index = dc_mode_to_region_index(cxled->mode);
> + if (dc_index >= 0) {
> + if (cxlds->dc_res[dc_index].child) {
> + dev_err(dev, "Cannot allocate DPA from DC Region: %d\n",
> + dc_index);
> + rc = -EINVAL;
> + goto out;
> + }
> + free_dc_start = cxlds->dc_res[dc_index].start;
> + }
> +
> if (cxled->mode == CXL_DECODER_RAM) {
> start = free_ram_start;
> avail = cxlds->ram_res.end - start + 1;
> @@ -521,12 +653,38 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
> else
> skip_end = start - 1;
> skip = skip_end - skip_start + 1;
> + } else if (cxl_decoder_mode_is_dc(cxled->mode)) {
> + resource_size_t skip_start, skip_end;
> +
> + start = free_dc_start;
> + avail = cxlds->dc_res[dc_index].end - start + 1;
> + if ((resource_size(&cxlds->pmem_res) == 0) || !cxlds->pmem_res.child)
> + skip_start = free_ram_start;
> + else
> + skip_start = free_pmem_start;
> + /*
> + * If any dc region is already mapped, then that allocation
> + * already handled the RAM and PMEM skip. Check for DC region
> + * skip.
> + */
> + for (int i = dc_index - 1; i >= 0 ; i--) {
> + if (cxlds->dc_res[i].child) {
> + skip_start = cxlds->dc_res[i].child->end + 1;
> + break;
> + }
> + }
> +
> + skip_end = start - 1;
> + skip = skip_end - skip_start + 1;

I notice in the pmem equivalent there is a case for part of the region already mapped.
Can that not happen for a DC region as well?

> } else {
> dev_dbg(dev, "mode not set\n");
> rc = -EINVAL;
> goto out;
> }
>
> + dev_dbg(dev, "DPA Allocation start: %pa len: %#llx Skip: %pa\n",
> + &start, size, &skip);
> +
> if (size > avail) {
> dev_dbg(dev, "%pa exceeds available %s capacity: %pa\n", &size,
> cxled->mode == CXL_DECODER_RAM ? "ram" : "pmem",