From 4fa4302d6dc7de7e8e74dc7405611a2efb4bf54b Mon Sep 17 00:00:00 2001 From: Fan Ni Date: Thu, 15 Dec 2022 17:09:14 +0000 Subject: [PATCH 1/2] cxl/region: Fix null pointer dereference for resetting decoder 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") Cc: Signed-off-by: Fan Ni Reviewed-by: Davidlohr Bueso Reviewed-by: Dave Jiang Reviewed-by: Jonathan Cameron Tested-by: Gregory Price Reviewed-by: Gregory Price Link: https://lore.kernel.org/r/20221215170909.2650271-1-fan.ni@samsung.com Signed-off-by: Dan Williams --- 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 02f28da519e3..02275e6b621b 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); From 711442e29f16f0d39dd0e2460c9baacfccb9d5a7 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Tue, 7 Feb 2023 11:04:30 -0800 Subject: [PATCH 2/2] cxl/region: Fix passthrough-decoder detection A passthrough decoder is a decoder that maps only 1 target. It is a special case because it does not impose any constraints on the interleave-math as compared to a decoder with multiple targets. Extend the passthrough case to multi-target-capable decoders that only have one target selected. I.e. the current code was only considering passthrough *ports* which are only a subset of the potential passthrough decoder scenarios. Fixes: e4f6dfa9ef75 ("cxl/region: Fix 'distance' calculation with passthrough ports") Cc: Reviewed-by: Dave Jiang Link: https://lore.kernel.org/r/167564540422.847146.13816934143225777888.stgit@dwillia2-xfh.jf.intel.com Signed-off-by: Dan Williams --- drivers/cxl/core/region.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c index 02275e6b621b..940f805b1534 100644 --- a/drivers/cxl/core/region.c +++ b/drivers/cxl/core/region.c @@ -993,10 +993,10 @@ static int cxl_port_setup_targets(struct cxl_port *port, int i, distance; /* - * Passthrough ports impose no distance requirements between + * Passthrough decoders impose no distance requirements between * peers */ - if (port->nr_dports == 1) + if (cxl_rr->nr_targets == 1) distance = 0; else distance = p->nr_targets / cxl_rr->nr_targets;