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hw/usb/hcd-xhci: fix interval alignment after MFINDEX passes 2^32

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epctx->interval is an unsigned int, so ~(epctx->interval - 1) is a
32-bit mask that is zero-extended when and-ed with the 64-bit microframe
index. Once mfindex no longer fits in 32 bits (2^32 * 125us, about 6.2
days after the controller was started), asap loses its upper half and
always compares below mfindex. Isoch TDs with SIA are then run at once
instead of at the next interval boundary. xhci_calc_intr_kick() has the
same expression.

Use ROUND_UP(), which builds the mask in the type of mfindex. The
interval is always a power of two.

The reporter of #3973 also saw the symptom with UHCI. This change does
not explain that.

Fixes: 3d1396842d ("xhci: iso xfer support")
Fixes: 4d7a81c06f ("xhci: emulate intr endpoint intervals correctly")
Link: https://gitlab.com/qemu-project/qemu/-/issues/3973
Cc: qemu-stable@nongnu.org
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Message-ID: <52c9f935428f2cfc65e4dee7e37638fcb965c6b2.1789968699.git.junjie.cao@intel.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Junjie Cao authored and Thomas Huth committed 2026-09-23 15:49:32 +02:00
1 parent ba920c1a0c
commit bfb82d57e7
1 file changed
+2 -4
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hw/usb/hcd-xhci.c
+2 -4
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@@ -1756,8 +1756,7 @@ static int xhci_fire_ctl_transfer(XHCIState *xhci, XHCITransfer *xfer)
static void xhci_calc_intr_kick(XHCIState *xhci, XHCITransfer *xfer,
XHCIEPContext *epctx, uint64_t mfindex)
{
uint64_t asap = ((mfindex + epctx->interval - 1) &
~(epctx->interval-1));
uint64_t asap = ROUND_UP(mfindex, epctx->interval);
uint64_t kick = epctx->mfindex_last + epctx->interval;
assert(epctx->interval != 0);
@@ -1768,8 +1767,7 @@ static void xhci_calc_iso_kick(XHCIState *xhci, XHCITransfer *xfer,
XHCIEPContext *epctx, uint64_t mfindex)
{
if (xfer->trbs[0].control & TRB_TR_SIA) {
uint64_t asap = ((mfindex + epctx->interval - 1) &
~(epctx->interval-1));
uint64_t asap = ROUND_UP(mfindex, epctx->interval);
if (asap >= epctx->mfindex_last &&
asap <= epctx->mfindex_last + epctx->interval * 4) {
xfer->mfindex_kick = epctx->mfindex_last + epctx->interval;