Messages in this thread | | | Date | Fri, 16 Feb 2024 13:10:14 +0100 | From | Robert Richter <> | Subject | Re: [PATCH v3 2/3] cxl/pci: Get rid of pointer arithmetic reading CDAT table |
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Hi Jonathan,
thanks for your review.
On 14.02.24 17:31:58, Jonathan Cameron wrote: > On Fri, 9 Feb 2024 20:26:46 +0100 > Robert Richter <rrichter@amd.com> wrote: > > > Reading the CDAT table using DOE requires a Table Access Response > > Header in addition to the CDAT entry. In current implementation this > > has caused offsets with sizeof(__le32) to the actual buffers. This led > > to hardly readable code and even bugs. E.g., see fix of devm_kfree() > > in read_cdat_data(): > > > > c65efe3685f5 cxl/cdat: Free correct buffer on checksum error > > > > Rework code to avoid calculations with sizeof(__le32). Introduce > > struct cdat_doe_rsp for this which contains the Table Access Response > > Header and a variable payload size for various data structures > > afterwards to access the CDAT table and its CDAT Data Structures > > without recalculating buffer offsets. > > > > Cc: Lukas Wunner <lukas@wunner.de> > > Cc: Fan Ni <nifan.cxl@gmail.com> > > Reviewed-by: Dave Jiang <dave.jiang@intel.com> > > Signed-off-by: Robert Richter <rrichter@amd.com> > > Hi Robert, > > I like this in general. A few comments inline though. > > > --- > > drivers/cxl/core/pci.c | 75 ++++++++++++++++++++++-------------------- > > drivers/cxl/cxlpci.h | 20 +++++++++++ > > 2 files changed, 59 insertions(+), 36 deletions(-) > > > > diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c > > index 39366ce94985..569354a5536f 100644 > > --- a/drivers/cxl/core/pci.c > > +++ b/drivers/cxl/core/pci.c > > @@ -544,55 +544,55 @@ static int cxl_cdat_get_length(struct device *dev, > > > > static int cxl_cdat_read_table(struct device *dev, > > struct pci_doe_mb *doe_mb, > > - void *cdat_table, size_t *cdat_length) > > + struct cdat_doe_rsp *rsp, size_t *length) > > Nitpick, but rsp isn't a response, it's the whole table. > Maybe it's worth a > #define cdat_doe_table cdat_doe_rsp > or a typedef so the two are different in name at least whilst sharing > same structure definition?
There is a comment near the kzalloc of buf. I think introducing another type here for single use will just add confusion.
I will also update the description of cdat_doe_rsp.
> > > { > > - size_t length = *cdat_length + sizeof(__le32); > > - __le32 *data = cdat_table; > > - int entry_handle = 0; > > + size_t received, remaining = *length; > > + unsigned int entry_handle = 0; > > + union cdat_data *data; > > __le32 saved_dw = 0; > > > > do { > > __le32 request = CDAT_DOE_REQ(entry_handle); > > - struct cdat_entry_header *entry; > > - size_t entry_dw; > > int rc; > > > > rc = pci_doe(doe_mb, PCI_DVSEC_VENDOR_ID_CXL, > > CXL_DOE_PROTOCOL_TABLE_ACCESS, > > &request, sizeof(request), > > - data, length); > > + rsp, sizeof(*rsp) + remaining); > > I guess it's not really worth using struct_size here. > It's main advantage is making it clear we are dealing with a > trailing []
Yes, will keep it as is. Since it's a u8 array, count is equal the size for the remaining data and we do not need struct_size() here.
> > > if (rc < 0) { > > dev_err(dev, "DOE failed: %d", rc); > > return rc; > > } > > > > - /* 1 DW Table Access Response Header + CDAT entry */ > > - entry = (struct cdat_entry_header *)(data + 1); > > - if ((entry_handle == 0 && > > - rc != sizeof(__le32) + sizeof(struct cdat_header)) || > > - (entry_handle > 0 && > > - (rc < sizeof(__le32) + sizeof(*entry) || > > - rc != sizeof(__le32) + le16_to_cpu(entry->length)))) > > + if (rc < sizeof(*rsp)) > > + return -EIO; > > + > > + data = (void *)rsp->data; > > Nicer to cast to (union cdat_data *) than rely on bounce via a void *
Will change.
> > > + received = rc - sizeof(*rsp); > > + > > + if ((!entry_handle && > > Prefer == 0 for this because 0 is a magic value here. > > > + received != sizeof(data->header)) || > > + (entry_handle && > > + (received < sizeof(data->entry) || > > + received != le16_to_cpu(data->entry.length)))) > > return -EIO; > > Given it's two rather involved conditions maybe better to do. > > if (entry_handle == 0) { > if (received != sizeof(data->header) > return -EIO; > } else { > if (received < sizeof(data->entry) || > received != le16_to_cpu(data->entry.length)) > return -EIO; > } > > More code but easier to see the header vs entry checks. > Could even define a little utility function / macro. > > cdat_is_head_handle(val) entry_handle == 0 > so you get somewhat more self documenting code. > > if (cdat_is_head_handle(entry_handle)) { > } else { > }
I will take this but without the macro.
> > > > > /* Get the CXL table access header entry handle */ > > entry_handle = FIELD_GET(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, > > - le32_to_cpu(data[0])); > > - entry_dw = rc / sizeof(__le32); > > - /* Skip Header */ > > - entry_dw -= 1; > > + le32_to_cpu(rsp->doe_header)); > > + > > /* > > * Table Access Response Header overwrote the last DW of > > * previous entry, so restore that DW > > */ > > - *data = saved_dw; > > - length -= entry_dw * sizeof(__le32); > > - data += entry_dw; > > - saved_dw = *data; > > + rsp->doe_header = saved_dw; > > I'm not keen on this looking like we are writing the doe header > as we are writing the tail of the last response. > > Maybe the comment is enough. I don't have a better idea on how > to make this more obvious.
I think the comment is good enough here.
> > > + remaining -= received; > > + rsp = (void *)rsp + received; > > Was a potential problem with previous code, but this could > in theory become unaligned and we should be using unaligned accessors > for it as a result, or maybe adding a check that it doesn't ever become so. > The check is probably the easier path given CDAT entries are thankfully > (I think) all dword multiples as are the two headers.
Yes, buffers are dwords. In any case, pci_doe_recv_resp() is safe to be used unaligned anyway.
Thanks for your review, will prepare a v4.
-Robert
> > > + saved_dw = rsp->doe_header; > > } while (entry_handle != CXL_DOE_TABLE_ACCESS_LAST_ENTRY); > > > > /* Length in CDAT header may exceed concatenation of CDAT entries */ > > - *cdat_length -= length - sizeof(__le32); > > + *length -= remaining; > > > > return 0; > > } > >
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