Messages in this thread Patch in this message | | | Date | Fri, 13 Jan 2023 11:01:08 +0000 | From | Jonathan Cameron <> | Subject | Re: [PATCH] cxl/region: Fix null pointer dereference for resetting decoder |
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On Thu, 15 Dec 2022 17:09:14 +0000 Fan Ni <fan.ni@samsung.com> wrote:
> Not all decoders have a reset callback. > > The CXL specification allows a host bridge with a single root port to > have no explicit HDM decoders. Currently the region driver assumes there > are none. As such the CXL core creates a special pass through decoder > instance without a commit/reset callback. > > Prior to this patch, the ->reset() callback was called unconditionally when > calling cxl_region_decode_reset. Thus a configuration with 1 Host Bridge, > 1 Root Port, and one directly attached CXL type 3 device or multiple CXL > type 3 devices attached to downstream ports of a switch can cause a null > pointer dereference. > > Before the fix, a kernel crash was observed when we destroy the region, and > a pass through decoder is reset. > > The issue can be reproduced as below, > 1) create a region with a CXL setup which includes a HB with a > single root port under which a memdev is attached directly. > 2) destroy the region with cxl destroy-region regionX -f. > > Fixes: 176baefb2eb5 ("cxl/hdm: Commit decoder state to hardware") > Signed-off-by: Fan Ni <fan.ni@samsung.com>
Explanation seems correct to me. Only question (and it's one for the Maintainers) is whether they prefer optionality here or a stub reset() implementation for the pass through decoder.
either way Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> --- > drivers/cxl/core/region.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c > index f9ae5ad284ff..3931793a13ac 100644 > --- a/drivers/cxl/core/region.c > +++ b/drivers/cxl/core/region.c > @@ -131,7 +131,7 @@ static int cxl_region_decode_reset(struct cxl_region *cxlr, int count) > struct cxl_memdev *cxlmd = cxled_to_memdev(cxled); > struct cxl_port *iter = cxled_to_port(cxled); > struct cxl_ep *ep; > - int rc; > + int rc = 0; > > while (!is_cxl_root(to_cxl_port(iter->dev.parent))) > iter = to_cxl_port(iter->dev.parent); > @@ -143,7 +143,8 @@ static int cxl_region_decode_reset(struct cxl_region *cxlr, int count) > > cxl_rr = cxl_rr_load(iter, cxlr); > cxld = cxl_rr->decoder; > - rc = cxld->reset(cxld); > + if (cxld->reset) > + rc = cxld->reset(cxld); > if (rc) > return rc; > } > @@ -186,7 +187,8 @@ static int cxl_region_decode_commit(struct cxl_region *cxlr) > iter = ep->next, ep = cxl_ep_load(iter, cxlmd)) { > cxl_rr = cxl_rr_load(iter, cxlr); > cxld = cxl_rr->decoder; > - cxld->reset(cxld); > + if (cxld->reset) > + cxld->reset(cxld); > } > > cxled->cxld.reset(&cxled->cxld);
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