scsi: mpt3sas: Block PCI config access from userspace during reset

While diag reset is in progress there is short duration where all access to
controller's PCI config space from the host needs to be blocked. This is
due to a hardware limitation of the IOC controllers.

Block all access to controller's config space from userland applications by
calling pci_cfg_access_lock() while diag reset is in progress and unlocking
it again after the controller comes back to ready state.

Link: https://lore.kernel.org/r/20210330105137.20728-1-sreekanth.reddy@broadcom.com
Cc: stable@vger.kernel.org #v5.4.108+
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_base.c

@@ -7405,6 +7405,8 @@ _base_diag_reset(struct MPT3SAS_ADAPTER *ioc)
 
 	ioc_info(ioc, "sending diag reset !!\n");
 
+	pci_cfg_access_lock(ioc->pdev);
+
 	drsprintk(ioc, ioc_info(ioc, "clear interrupts\n"));
 
 	count = 0;
@@ -7495,10 +7497,12 @@ _base_diag_reset(struct MPT3SAS_ADAPTER *ioc)
 		goto out;
 	}
 
+	pci_cfg_access_unlock(ioc->pdev);
 	ioc_info(ioc, "diag reset: SUCCESS\n");
 	return 0;
 
  out:
+	pci_cfg_access_unlock(ioc->pdev);
 	ioc_err(ioc, "diag reset: FAILED\n");
 	return -EFAULT;
 }