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cxl/port: Fix missing target list lock 

[ Upstream commit 5459e186a5 ]

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: 27b3f8d138 ("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>
This commit is contained in:
Dan Williams 2023-12-21 21:05:01 -08:00 committed by Greg Kroah-Hartman
parent 4e0d679193
commit 1a5369728c
2 changed files with 7 additions and 17 deletions
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22
drivers/cxl/core/port.c
View File

@ -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);
}

2
drivers/cxl/cxl.h
View File

@ -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[];
};