Re: [PATCH 14/46] cxl/hdm: Enumerate allocated DPA

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: <linux-cxl@vger.kernel.org>, Ben Widawsky <bwidawsk@kernel.org>,
	<hch@infradead.org>, <alison.schofield@intel.com>,
	<nvdimm@lists.linux.dev>, <linux-pci@vger.kernel.org>,
	<patches@lists.linux.dev>
Subject: Re: [PATCH 14/46] cxl/hdm: Enumerate allocated DPA
Date: Wed, 29 Jun 2022 15:43:59 +0100	[thread overview]
Message-ID: <20220629154359.000021cc@Huawei.com> (raw)
In-Reply-To: <165603880411.551046.9204694225111844300.stgit@dwillia2-xfh>

On Thu, 23 Jun 2022 19:46:44 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> In preparation for provisioining CXL regions, add accounting for the DPA
> space consumed by existing regions / decoders. Recall, a CXL region is a
> memory range comrpised from one or more endpoint devices contributing a
> mapping of their DPA into HPA space through a decoder.
> 
> Record the DPA ranges covered by committed decoders at initial probe of
> endpoint ports relative to a per-device resource tree of the DPA type
> (pmem or volaltile-ram).
> 
> The cxl_dpa_rwsem semaphore is introduced to globally synchronize DPA
> state across all endpoints and their decoders at once. The vast majority
> of DPA operations are reads as region creation is expected to be as rare
> as disk partitioning and volume creation. The device_lock() for this
> synchronization is specifically avoided for concern of entangling with
> sysfs attribute removal.
> 
> Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/cxl/core/hdm.c |  148 ++++++++++++++++++++++++++++++++++++++++++++----
>  drivers/cxl/cxl.h      |    2 +
>  drivers/cxl/cxlmem.h   |   13 ++++
>  3 files changed, 152 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index c940a4911fee..daae6e533146 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -7,6 +7,8 @@
>  #include "cxlmem.h"
>  #include "core.h"
>  
> +static DECLARE_RWSEM(cxl_dpa_rwsem);

I've not checked many files, but pci.c has equivalent static defines after
the DOC: entry so for consistency move this below that?

> +
>  /**
>   * DOC: cxl core hdm
>   *
> @@ -128,10 +130,108 @@ struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port)
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_cxl_setup_hdm, CXL);
>  
> +/*
> + * Must be called in a context that synchronizes against this decoder's
> + * port ->remove() callback (like an endpoint decoder sysfs attribute)
> + */
> +static void cxl_dpa_release(void *cxled);
> +static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled, bool remove_action)
> +{
> +	struct cxl_port *port = cxled_to_port(cxled);
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> +	struct resource *res = cxled->dpa_res;
> +
> +	lockdep_assert_held_write(&cxl_dpa_rwsem);
> +
> +	if (remove_action)
> +		devm_remove_action(&port->dev, cxl_dpa_release, cxled);

This code organization is more surprising than I'd like. Why not move this to
a wrapper that is like devm_kfree() and similar which do the free now and
remove from the devm list?

static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
{
	struct cxl_port *port = cxled_to_port(cxled);
	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
	struct cxl_dev_state *cxlds = cxlmd->cxlds;
	struct resource *res = cxled->dpa_res;

	if (cxled->skip)
		__release_region(&cxlds->dpa_res, res->start - cxled->skip,
				 cxled->skip);
	cxled->skip = 0;
	__release_region(&cxlds->dpa_res, res->start, resource_size(res));
	cxled->dpa_res = NULL;
}

/* possibly add some underscores to this name to indicate it's special
   in when you can safely call it */
static void devm_cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
{
	struct cxl_port *port = cxled_to_port(cxled);
	lockdep_assert_held_write(&cxl_dpa_rwsem);
	devm_remove_action(&port->dev, cxl_dpa_release, cxled);
	__cxl_dpa_release(cxled);
}

static void cxl_dpa_release(void *cxled)
{
	down_write(&cxl_dpa_rwsem);
	__cxl_dpa_release(cxled, false);
	up_write(&cxl_dpa_rwsem);
}

> +
> +	if (cxled->skip)
> +		__release_region(&cxlds->dpa_res, res->start - cxled->skip,
> +				 cxled->skip);
> +	cxled->skip = 0;
> +	__release_region(&cxlds->dpa_res, res->start, resource_size(res));
> +	cxled->dpa_res = NULL;
> +}
> +
> +static void cxl_dpa_release(void *cxled)
> +{
> +	down_write(&cxl_dpa_rwsem);
> +	__cxl_dpa_release(cxled, false);
> +	up_write(&cxl_dpa_rwsem);
> +}
> +
> +static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> +			     resource_size_t base, resource_size_t len,
> +			     resource_size_t skip)
> +{
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_port *port = cxled_to_port(cxled);
> +	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> +	struct device *dev = &port->dev;
> +	struct resource *res;
> +
> +	lockdep_assert_held_write(&cxl_dpa_rwsem);
> +
> +	if (!len)
> +		return 0;
> +
> +	if (cxled->dpa_res) {
> +		dev_dbg(dev, "decoder%d.%d: existing allocation %pr assigned\n",
> +			port->id, cxled->cxld.id, cxled->dpa_res);
> +		return -EBUSY;
> +	}
> +
> +	if (skip) {
> +		res = __request_region(&cxlds->dpa_res, base - skip, skip,
> +				       dev_name(dev), 0);

Interface that uses a backwards definition of skip as what to skip before
the base parameter is a little odd can we rename base parameter to something
like 'current_top' then have base = current_top + skip?  current_top naming
not great though...

> +		if (!res) {
> +			dev_dbg(dev,
> +				"decoder%d.%d: failed to reserve skip space\n",
> +				port->id, cxled->cxld.id);
> +			return -EBUSY;
> +		}
> +	}
> +	res = __request_region(&cxlds->dpa_res, base, len, dev_name(dev), 0);
> +	if (!res) {
> +		dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
> +			port->id, cxled->cxld.id);
> +		if (skip)
> +			__release_region(&cxlds->dpa_res, base - skip, skip);
> +		return -EBUSY;
> +	}
> +	cxled->dpa_res = res;
> +	cxled->skip = skip;
> +
> +	return 0;
> +}
> +

...