6.15-stable review patch. If anyone has any objections, please let me know.
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From: Halil Pasic pasic@linux.ibm.com
[ Upstream commit 897e8601b9cff1d054cdd53047f568b0e1995726 ]
The s390x ISM device data sheet clearly states that only one request-response sequence is allowable per ISM function at any point in time. Unfortunately as of today the s390/ism driver in Linux does not honor that requirement. This patch aims to rectify that.
This problem was discovered based on Aliaksei's bug report which states that for certain workloads the ISM functions end up entering error state (with PEC 2 as seen from the logs) after a while and as a consequence connections handled by the respective function break, and for future connection requests the ISM device is not considered -- given it is in a dysfunctional state. During further debugging PEC 3A was observed as well.
A kernel message like [ 1211.244319] zpci: 061a:00:00.0: Event 0x2 reports an error for PCI function 0x61a is a reliable indicator of the stated function entering error state with PEC 2. Let me also point out that a kernel message like [ 1211.244325] zpci: 061a:00:00.0: The ism driver bound to the device does not support error recovery is a reliable indicator that the ISM function won't be auto-recovered because the ISM driver currently lacks support for it.
On a technical level, without this synchronization, commands (inputs to the FW) may be partially or fully overwritten (corrupted) by another CPU trying to issue commands on the same function. There is hard evidence that this can lead to DMB token values being used as DMB IOVAs, leading to PEC 2 PCI events indicating invalid DMA. But this is only one of the failure modes imaginable. In theory even completely losing one command and executing another one twice and then trying to interpret the outputs as if the command we intended to execute was actually executed and not the other one is also possible. Frankly, I don't feel confident about providing an exhaustive list of possible consequences.
Fixes: 684b89bc39ce ("s390/ism: add device driver for internal shared memory") Reported-by: Aliaksei Makarau Aliaksei.Makarau@ibm.com Tested-by: Mahanta Jambigi mjambigi@linux.ibm.com Tested-by: Aliaksei Makarau Aliaksei.Makarau@ibm.com Signed-off-by: Halil Pasic pasic@linux.ibm.com Reviewed-by: Alexandra Winter wintera@linux.ibm.com Signed-off-by: Alexandra Winter wintera@linux.ibm.com Reviewed-by: Simon Horman horms@kernel.org Link: https://patch.msgid.link/20250722161817.1298473-1-wintera@linux.ibm.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/s390/net/ism_drv.c | 3 +++ include/linux/ism.h | 1 + 2 files changed, 4 insertions(+)
diff --git a/drivers/s390/net/ism_drv.c b/drivers/s390/net/ism_drv.c index 60ed70a39d2cc..b8464d9433e96 100644 --- a/drivers/s390/net/ism_drv.c +++ b/drivers/s390/net/ism_drv.c @@ -130,6 +130,7 @@ static int ism_cmd(struct ism_dev *ism, void *cmd) struct ism_req_hdr *req = cmd; struct ism_resp_hdr *resp = cmd;
+ spin_lock(&ism->cmd_lock); __ism_write_cmd(ism, req + 1, sizeof(*req), req->len - sizeof(*req)); __ism_write_cmd(ism, req, 0, sizeof(*req));
@@ -143,6 +144,7 @@ static int ism_cmd(struct ism_dev *ism, void *cmd) } __ism_read_cmd(ism, resp + 1, sizeof(*resp), resp->len - sizeof(*resp)); out: + spin_unlock(&ism->cmd_lock); return resp->ret; }
@@ -606,6 +608,7 @@ static int ism_probe(struct pci_dev *pdev, const struct pci_device_id *id) return -ENOMEM;
spin_lock_init(&ism->lock); + spin_lock_init(&ism->cmd_lock); dev_set_drvdata(&pdev->dev, ism); ism->pdev = pdev; ism->dev.parent = &pdev->dev; diff --git a/include/linux/ism.h b/include/linux/ism.h index 5428edd909823..8358b4cd7ba6a 100644 --- a/include/linux/ism.h +++ b/include/linux/ism.h @@ -28,6 +28,7 @@ struct ism_dmb {
struct ism_dev { spinlock_t lock; /* protects the ism device */ + spinlock_t cmd_lock; /* serializes cmds */ struct list_head list; struct pci_dev *pdev;