[PATCH 2/3 for-next] pvscsi: Limit ring pages for swiotlb

[PATCH 2/3 for-next] pvscsi: Limit ring pages for swiotlb

[Jim Gill]

A large number of outstanding scsi commands can
 completely fill up the allowable DMA size. Typically this happens with
 SWIOTLB and SEV encryption active. While this is harmless for the scsi middle
 layer, it floods the kernel log with error messages and can cause other
 device drivers to error. Reduce the number of ring pages to 1 if we detect
 DMA size restrictions.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
[jgill@vmware.com: Forwarding patch on behalf of thellstrom]
Acked-by: jgill@vmware.com
---
 drivers/scsi/vmw_pvscsi.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/vmw_pvscsi.c b/drivers/scsi/vmw_pvscsi.c
index 0573e94..fa2748f 100644
--- a/drivers/scsi/vmw_pvscsi.c
+++ b/drivers/scsi/vmw_pvscsi.c
@@ -28,6 +28,7 @@
 #include <linux/workqueue.h>
 #include <linux/pci.h>
 #include <linux/dmapool.h>
+#include <linux/mem_encrypt.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_host.h>
@@ -45,6 +46,7 @@ MODULE_LICENSE("GPL");
 MODULE_VERSION(PVSCSI_DRIVER_VERSION_STRING);
 
 #define PVSCSI_DEFAULT_NUM_PAGES_PER_RING	8
+#define PVSCSI_RESTRICT_NUM_PAGES_PER_RING      1
 #define PVSCSI_DEFAULT_NUM_PAGES_MSG_RING	1
 #define PVSCSI_DEFAULT_QUEUE_DEPTH		254
 #define SGL_SIZE				PAGE_SIZE
@@ -1416,14 +1418,26 @@ static int pvscsi_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	max_id = pvscsi_get_max_targets(adapter);
 	printk(KERN_INFO "vmw_pvscsi: max_id: %u\n", max_id);
 
-	if (pvscsi_ring_pages == 0)
-		/*
-		 * Set the right default value. Up to 16 it is 8, above it is
-		 * max.
-		 */
-		pvscsi_ring_pages = (max_id > 16) ?
-			PVSCSI_SETUP_RINGS_MAX_NUM_PAGES :
-			PVSCSI_DEFAULT_NUM_PAGES_PER_RING;
+	if (pvscsi_ring_pages == 0) {
+		struct sysinfo si;
+
+		si_meminfo(&si);
+		if (mem_encrypt_active())
+			/*
+			 * There are DMA size restrictions. Reduce the queue
+			 * depth to try to avoid exhausting DMA size and trigger
+			 * dma mapping errors.
+			 */
+			pvscsi_ring_pages = PVSCSI_RESTRICT_NUM_PAGES_PER_RING;
+		else
+			/*
+			 * Set the right default value. Up to 16 it is 8,
+			 * above it is max.
+			 */
+			pvscsi_ring_pages = (max_id > 16) ?
+				PVSCSI_SETUP_RINGS_MAX_NUM_PAGES :
+				PVSCSI_DEFAULT_NUM_PAGES_PER_RING;
+	}
 	printk(KERN_INFO
 	       "vmw_pvscsi: setting ring_pages to %d\n",
 	       pvscsi_ring_pages);
-- 
2.7.4

Re: [PATCH 2/3 for-next] pvscsi: Limit ring pages for swiotlb

[Christoph Hellwig]

On Wed, Aug 12, 2020 at 01:55:02PM -0700, Jim Gill wrote:
> A large number of outstanding scsi commands can
>  completely fill up the allowable DMA size. Typically this happens with
>  SWIOTLB and SEV encryption active. While this is harmless for the scsi middle
>  layer, it floods the kernel log with error messages and can cause other
>  device drivers to error. Reduce the number of ring pages to 1 if we detect
>  DMA size restrictions.

Umm, no.  Drivers have absolutely no business checking
mem_encrypt_active().