cxl/port: Fix missing target list lock

[ Upstream commit 5459e186a5c9f412334321cff58d70dcb0e48a04 ]

cxl_port_setup_targets() modifies the ->targets[] array of a switch
decoder. target_list_show() expects to be able to emit a coherent
snapshot of that array by "holding" ->target_lock for read. The
target_lock is held for write during initialization of the ->targets[]
array, but it is not held for write during cxl_port_setup_targets().

The ->target_lock() predates the introduction of @cxl_region_rwsem. That
semaphore protects changes to host-physical-address (HPA) decode which
is precisely what writes to a switch decoder's target list affects.

Replace ->target_lock with @cxl_region_rwsem.

Now the side-effect of snapshotting a unstable view of a decoder's
target list is likely benign so the Fixes: tag is presumptive.

Fixes: 27b3f8d13830 ("cxl/region: Program target lists")
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 4081052bb38576942c515ce37a435cb9ad5346ab..c67cc8c9d5cc61bfe5d27ec470ef92b97c1e6aa2 100644 (file)
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -172,14 +172,10 @@ static ssize_t target_list_show(struct device *dev,
 {
        struct cxl_switch_decoder *cxlsd = to_cxl_switch_decoder(dev);
        ssize_t offset;
-       unsigned int seq;
        int rc;
 
-       do {
-               seq = read_seqbegin(&cxlsd->target_lock);
-               rc = emit_target_list(cxlsd, buf);
-       } while (read_seqretry(&cxlsd->target_lock, seq));
-
+       guard(rwsem_read)(&cxl_region_rwsem);
+       rc = emit_target_list(cxlsd, buf);
        if (rc < 0)
                return rc;
        offset = rc;
@@ -1579,7 +1575,7 @@ EXPORT_SYMBOL_NS_GPL(cxl_mem_find_port, CXL);
 static int decoder_populate_targets(struct cxl_switch_decoder *cxlsd,
                                    struct cxl_port *port, int *target_map)
 {
-       int i, rc = 0;
+       int i;
 
        if (!target_map)
                return 0;
@@ -1589,19 +1585,16 @@ static int decoder_populate_targets(struct cxl_switch_decoder *cxlsd,
        if (xa_empty(&port->dports))
                return -EINVAL;
 
-       write_seqlock(&cxlsd->target_lock);
+       guard(rwsem_write)(&cxl_region_rwsem);
        for (i = 0; i < cxlsd->cxld.interleave_ways; i++) {
                struct cxl_dport *dport = find_dport(port, target_map[i]);
 
-               if (!dport) {
-                       rc = -ENXIO;
-                       break;
-               }
+               if (!dport)
+                       return -ENXIO;
                cxlsd->target[i] = dport;
        }
-       write_sequnlock(&cxlsd->target_lock);
 
-       return rc;
+       return 0;
 }
 
 struct cxl_dport *cxl_hb_modulo(struct cxl_root_decoder *cxlrd, int pos)
@@ -1671,7 +1664,6 @@ static int cxl_switch_decoder_init(struct cxl_port *port,
                return -EINVAL;
 
        cxlsd->nr_targets = nr_targets;
-       seqlock_init(&cxlsd->target_lock);
        return cxl_decoder_init(port, &cxlsd->cxld);
 }
 

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 6c6afda0e4c611c294e15335a902aaf96a15151a..de2c250c894b10ae0f7fa21aa6d5c798c4162ee0 100644 (file)
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -404,7 +404,6 @@ struct cxl_endpoint_decoder {
 /**
  * struct cxl_switch_decoder - Switch specific CXL HDM Decoder
  * @cxld: base cxl_decoder object
- * @target_lock: coordinate coherent reads of the target list
  * @nr_targets: number of elements in @target
  * @target: active ordered target list in current decoder configuration
  *
@@ -416,7 +415,6 @@ struct cxl_endpoint_decoder {
  */
 struct cxl_switch_decoder {
        struct cxl_decoder cxld;
-       seqlock_t target_lock;
        int nr_targets;
        struct cxl_dport *target[];
 };