[Qemu-devel] [PULL 1/4] xhci: Avoid DMA when ERSTBA is set to zero

[Gerd Hoffmann <kraxel@redhat.com>]

From: Alexey Kardashevskiy <aik@ozlabs.ru>

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>
---
 hw/usb/hcd-xhci.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 204ea69d3f..d75c085d94 100644
--- 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);
-- 
2.9.3