xhci: Avoid DMA when ERSTBA is set to zero

The existing XHCI code reads the Event Ring Segment Table Base Address
Register (ERSTBA) every time when it is changed. However zero is its
default state so one would think that zero there means it is not in use.

This adds a check for ERSTBA in addition to the existing check for
the Event Ring Segment Table Size Register (ERSTSZ).

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-id: 20170911065606.40600-1-aik@ozlabs.ru
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 204ea69d3f59bb47c485be0214e8abc3d4f833bf..d75c085d94426270ac1a8483077afc9f865d883f 100644 (file)
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -811,8 +811,9 @@ static void xhci_er_reset(XHCIState *xhci, int v)
 {
     XHCIInterrupter *intr = &xhci->intr[v];
     XHCIEvRingSeg seg;
+    dma_addr_t erstba = xhci_addr64(intr->erstba_low, intr->erstba_high);
 
-    if (intr->erstsz == 0) {
+    if (intr->erstsz == 0 || erstba == 0) {
         /* disabled */
         intr->er_start = 0;
         intr->er_size = 0;
@@ -824,7 +825,6 @@ static void xhci_er_reset(XHCIState *xhci, int v)
         xhci_die(xhci);
         return;
     }
-    dma_addr_t erstba = xhci_addr64(intr->erstba_low, intr->erstba_high);
     pci_dma_read(PCI_DEVICE(xhci), erstba, &seg, sizeof(seg));
     le32_to_cpus(&seg.addr_low);
     le32_to_cpus(&seg.addr_high);