| Message ID | 20230111101054.188136-1-yishaih@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V1] lib/scatterlist: Fix to calculate the last_pg properly | expand |
On 1/11/23 02:10, Yishai Hadas wrote: > The last_pg is wrong, it is actually the first page of the last > scatterlist element. To get the last page of the last scatterlist > element we have to add prv->length. So it is checking mergability > against the wrong page, Further, a SG element is not guaranteed to end > on a page boundary, so we have to check the sub page location also for > merge eligibility. > > Fix the above by checking physical contiguity based on PFNs, compute the > actual last page and then call pages_are_mergable(). > > Fixes: 1567b49d1a40 ("lib/scatterlist: add check when merging zone device pages") > Reported-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Yishai Hadas <yishaih@nvidia.com> > --- Looks good. Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com> -ck
On Wed, Jan 11, 2023 at 12:10:54PM +0200, Yishai Hadas wrote: > The last_pg is wrong, it is actually the first page of the last > scatterlist element. To get the last page of the last scatterlist > element we have to add prv->length. So it is checking mergability > against the wrong page, Further, a SG element is not guaranteed to end > on a page boundary, so we have to check the sub page location also for > merge eligibility. > > Fix the above by checking physical contiguity based on PFNs, compute the > actual last page and then call pages_are_mergable(). > > Fixes: 1567b49d1a40 ("lib/scatterlist: add check when merging zone device pages") > Reported-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Yishai Hadas <yishaih@nvidia.com> Applied to rdma for-rc Thanks, Jason
diff --git a/lib/scatterlist.c b/lib/scatterlist.c index f72aa50c6654..8d7519a8f308 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -470,22 +470,27 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append, return -EOPNOTSUPP; if (sgt_append->prv) { + unsigned long next_pfn = (page_to_phys(sg_page(sgt_append->prv)) + + sgt_append->prv->offset + sgt_append->prv->length) / PAGE_SIZE; + if (WARN_ON(offset)) return -EINVAL; /* Merge contiguous pages into the last SG */ prv_len = sgt_append->prv->length; - last_pg = sg_page(sgt_append->prv); - while (n_pages && pages_are_mergeable(pages[0], last_pg)) { - if (sgt_append->prv->length + PAGE_SIZE > max_segment) - break; - sgt_append->prv->length += PAGE_SIZE; - last_pg = pages[0]; - pages++; - n_pages--; + if (page_to_pfn(pages[0]) == next_pfn) { + last_pg = pfn_to_page(next_pfn - 1); + while (n_pages && pages_are_mergeable(pages[0], last_pg)) { + if (sgt_append->prv->length + PAGE_SIZE > max_segment) + break; + sgt_append->prv->length += PAGE_SIZE; + last_pg = pages[0]; + pages++; + n_pages--; + } + if (!n_pages) + goto out; } - if (!n_pages) - goto out; } /* compute number of contiguous chunks */
The last_pg is wrong, it is actually the first page of the last scatterlist element. To get the last page of the last scatterlist element we have to add prv->length. So it is checking mergability against the wrong page, Further, a SG element is not guaranteed to end on a page boundary, so we have to check the sub page location also for merge eligibility. Fix the above by checking physical contiguity based on PFNs, compute the actual last page and then call pages_are_mergable(). Fixes: 1567b49d1a40 ("lib/scatterlist: add check when merging zone device pages") Reported-by: Jason Gunthorpe <jgg@nvidia.com> Signed-off-by: Yishai Hadas <yishaih@nvidia.com> --- Changelog: v1: * Rename 'paddr' to 'next_pfn' as it's actually. * Move to use page_to_phys() to clarify the code. * Fix to use (next_pfn - 1) instead of (paddr - PAGE_SIZE). v0: https://lore.kernel.org/lkml/Y7zyyTxdoJulq7OD@casper.infradead.org/T/ lib/scatterlist.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-)