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Date:   Wed, 8 Jun 2022 17:34:24 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Ben Widawsky <bwidawsk@kernel.org>
CC:     Dan Williams <dan.j.williams@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        "Alison Schofield" <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-cxl@vger.kernel.org>,
        <linux-pci@vger.kernel.org>
Subject: Re: [PATCH V10 9/9] cxl/port: Parse out DSMAS data from CDAT table
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References: <20220605005049.2155874-1-ira.weiny@intel.com>
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 <20220606193220.aw7ouwtop7lo2gpc@bwidawsk-mobl5>
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On Mon, Jun 06, 2022 at 12:32:20PM -0700, Ben Widawsky wrote:
> On 22-06-04 17:50:49, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> > 
> > CXL Ports with memory devices attached need the information from the
> > Device Scoped Memory Affinity Structure (DSMAS).  This information is
> > contained within the CDAT table buffer which is previously read and
> > cached in the port device.
> > 
> > If CDAT data is available, parse and cache DSMAS data from the table.
> > Store this data in unmarshaled struct dsmas data structures for ease of
> > use later.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > 
> > ---
> > Changes from V8
> > 	Adjust to the cdat data being in cxl_port
> > 
> > Changes from V7
> > 	Rebased on cxl-pending
> > 
> > Changes from V6
> > 	Move to port.c
> > 	It is not an error if no DSMAS data is found
> > 
> > Changes from V5
> > 	Fix up sparse warnings
> > 	Split out cdat_hdr_valid()
> > 	Update cdat_hdr_valid()
> > 		Remove revision and cs field parsing
> > 			There is no point in these
> > 		Add seq check and debug print.
> > 	From Jonathan
> > 		Add spaces around '+' and '/'
> > 		use devm_krealloc() for dmas_ary
> > ---
> >  drivers/cxl/cdat.h     | 17 +++++++++++
> >  drivers/cxl/core/pci.c | 65 ++++++++++++++++++++++++++++++++++++++++++
> >  drivers/cxl/cxl.h      |  2 ++
> >  drivers/cxl/cxlmem.h   |  4 +++
> >  drivers/cxl/cxlpci.h   |  1 +
> >  drivers/cxl/mem.c      |  1 +
> >  6 files changed, 90 insertions(+)
> > 
> > diff --git a/drivers/cxl/cdat.h b/drivers/cxl/cdat.h
> > index 3d8945612511..0a510f73fe6d 100644
> > --- a/drivers/cxl/cdat.h
> > +++ b/drivers/cxl/cdat.h
> > @@ -85,6 +85,23 @@
> >  
> >  #define CXL_DOE_PROTOCOL_TABLE_ACCESS 2
> >  
> > +/**
> > + * struct cxl_dsmas - host unmarshaled version of DSMAS data
> > + *
> > + * As defined in the Coherent Device Attribute Table (CDAT) specification this
> > + * represents a single DSMAS entry in that table.
> > + *
> > + * @dpa_base: The lowest Device Physical Address associated with this DSMAD
> > + * @length: Length in bytes of this DSMAD
> > + * @non_volatile: If set, the memory region represents Non-Volatile memory
> > + */
> > +struct cxl_dsmas {
> > +	u64 dpa_base;
> > +	u64 length;
> > +	/* Flags */
> > +	u8 non_volatile:1;
> > +};
> > +
> >  /**
> >   * struct cxl_cdat - CXL CDAT data
> >   *
> > diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> > index e68f13e66fcf..9666cc4a67aa 100644
> > --- a/drivers/cxl/core/pci.c
> > +++ b/drivers/cxl/core/pci.c
> > @@ -673,3 +673,68 @@ void read_cdat_data(struct cxl_port *port)
> >  		retries);
> >  }
> >  EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
> > +
> > +void parse_dsmas(struct cxl_memdev *cxlmd, struct cxl_port *port)
> > +{
> > +	struct device *dev = &port->dev;
> > +	struct cxl_dsmas *dsmas_ary = NULL;
> > +	u32 *data = port->cdat.table;
> > +	int bytes_left = port->cdat.length;
> > +	int nr_dsmas = 0;
> > +
> > +	if (!data) {
> > +		dev_info(dev, "No CDAT data available for DSMAS\n");
> > +		return;
> > +	}
> > +
> > +	/* Skip header */
> > +	data += CDAT_HEADER_LENGTH_DW;
> > +	bytes_left -= CDAT_HEADER_LENGTH_BYTES;
> > +
> > +	while (bytes_left > 0) {
> > +		u32 *cur_rec = data;
> > +		u8 type = FIELD_GET(CDAT_STRUCTURE_DW0_TYPE, cur_rec[0]);
> > +		u16 length = FIELD_GET(CDAT_STRUCTURE_DW0_LENGTH, cur_rec[0]);
> > +
> > +		if (type == CDAT_STRUCTURE_DW0_TYPE_DSMAS) {
> > +			struct cxl_dsmas *new_ary;
> > +			u8 flags;
> > +
> > +			new_ary = devm_krealloc(dev, dsmas_ary,
> > +					   sizeof(*dsmas_ary) * (nr_dsmas + 1),
> > +					   GFP_KERNEL);
> > +			if (!new_ary) {
> > +				dev_err(dev,
> > +					"Failed to allocate memory for DSMAS data (nr_dsmas %d)\n",
> > +					nr_dsmas);
> > +				return;
> > +			}
> > +			dsmas_ary = new_ary;
> 
> I don't love the realloc on every loop (though I've done something similar
> before). What about allocating enough entries port->cdat.length, and then a
> single krealloc to shorten the array upon success? I think krealloc pretty much
> always succeeds when you shrink FWIW.

I'm not sure that it would be better in any significant way honestly.  The
chances of krealloc failing is small.

> 
> > +
> > +			flags = FIELD_GET(CDAT_DSMAS_DW1_FLAGS, cur_rec[1]);
> 
> Does it make sense to test length/bytes_left before reading cur_rec[1]?

Interesting idea.  On the one hand the CDAT was already validated with the
checksum.  But the checksum could be valid even if the dsmas data was
corrupted.  Especially by a malicious device.  Also, I'm not sure but I think
SPDM would protect us from malicious devices once implemented.

Overall, it seems like checking bytes_left is a good check to ensure we don't
run off the end of our buffer even if it is just some fluke of data reads.

As to length I'm not seeing a danger but it might be nice to know that
something in the dsmas header was wrong.  I'll think on this more.

> 
> > +
> > +			dsmas_ary[nr_dsmas].dpa_base = CDAT_DSMAS_DPA_OFFSET(cur_rec);
> > +			dsmas_ary[nr_dsmas].length = CDAT_DSMAS_DPA_LEN(cur_rec);
> > +			dsmas_ary[nr_dsmas].non_volatile = CDAT_DSMAS_NON_VOLATILE(flags);
> > +
> > +			dev_dbg(dev, "DSMAS %d: %llx:%llx %s\n",
> > +				nr_dsmas,
> > +				dsmas_ary[nr_dsmas].dpa_base,
> > +				dsmas_ary[nr_dsmas].dpa_base +
> > +					dsmas_ary[nr_dsmas].length,
> > +				(dsmas_ary[nr_dsmas].non_volatile ?
> > +					"Persistent" : "Volatile")
> > +				);
> > +
> > +			nr_dsmas++;
> > +		}
> > +
> > +		data += (length / sizeof(u32));
> > +		bytes_left -= length;
> > +	}
> > +
> > +	dev_dbg(dev, "Found %d DSMAS entries\n", nr_dsmas);
> > +	cxlmd->dsmas_ary = dsmas_ary;
> > +	cxlmd->nr_dsmas = nr_dsmas;
> > +}
> > +EXPORT_SYMBOL_NS_GPL(parse_dsmas, CXL);
> > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > index 531b77d296c7..4d779a8fb807 100644
> > --- a/drivers/cxl/cxl.h
> > +++ b/drivers/cxl/cxl.h
> > @@ -10,6 +10,8 @@
> >  #include <linux/io.h>
> >  #include "cdat.h"
> >  
> > +#include "cdat.h"
> > +
> >  /**
> >   * DOC: cxl objects
> >   *
> > diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> > index 4d2764b865ab..ce5b00f3ebcb 100644
> > --- a/drivers/cxl/cxlmem.h
> > +++ b/drivers/cxl/cxlmem.h
> > @@ -36,6 +36,8 @@
> >   * @cxlds: The device state backing this device
> >   * @detach_work: active memdev lost a port in its ancestry
> >   * @id: id number of this memdev instance.
> > + * @dsmas_ary: Array of DSMAS entries as parsed from the CDAT table
> > + * @nr_dsmas: Number of entries in dsmas_ary
> 
> Personally don't think it's necessary to append "_ary". Up to you.

I think it's fine.

Thanks for the review,
Ira