powerpc/pseries: Fix handling of PLPKS object flushing timeout

plpks_confirm_object_flushed() uses the H_PKS_CONFIRM_OBJECT_FLUSHED hcall
to check whether changes to an object in the Platform KeyStore have been
flushed to non-volatile storage.

The hcall returns two output values, the return code and the flush status.
plpks_confirm_object_flushed() polls the hcall until either the flush
status has updated, the return code is an error, or a timeout has been
exceeded.

While we're still polling, the hcall is returning H_SUCCESS (0) as the
return code. In the timeout case, this means that upon exiting the polling
loop, rc is 0, and therefore 0 is returned to the user.

Handle the timeout case separately and return ETIMEDOUT if triggered.

Fixes: 2454a7af ("powerpc/pseries: define driver for Platform KeyStore")
Reported-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Tested-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-2-ajd@linux.ibm.com

arch/powerpc/platforms/pseries/plpks.c

@@ -248,6 +248,7 @@ static int plpks_confirm_object_flushed(struct label *label,
 					struct plpks_auth *auth)
 {
 	unsigned long retbuf[PLPAR_HCALL_BUFSIZE] = { 0 };
+	bool timed_out = true;
 	u64 timeout = 0;
 	u8 status;
 	int rc;
@@ -259,22 +260,26 @@ static int plpks_confirm_object_flushed(struct label *label,
 
 		status = retbuf[0];
 		if (rc) {
+			timed_out = false;
 			if (rc == H_NOT_FOUND && status == 1)
 				rc = 0;
 			break;
 		}
 
-		if (!rc && status == 1)
+		if (!rc && status == 1) {
+			timed_out = false;
 			break;
+		}
 
 		usleep_range(PKS_FLUSH_SLEEP,
 			     PKS_FLUSH_SLEEP + PKS_FLUSH_SLEEP_RANGE);
 		timeout = timeout + PKS_FLUSH_SLEEP;
 	} while (timeout < PKS_FLUSH_MAX_TIMEOUT);
 
-	rc = pseries_status_to_err(rc);
+	if (timed_out)
+		return -ETIMEDOUT;
 
-	return rc;
+	return pseries_status_to_err(rc);
 }
 
 int plpks_write_var(struct plpks_var var)