Public bug reported: I believe that the Event Ring handling in QEMU is not correct. For example, an Event Ring may have multiple segments. However, the code in xhci_write_event() (https://git.qemu.org/?p=qemu.git;a=blob;f=hw/usb /hcd-xhci.c;hb=HEAD#l645), starting with line 668, seems to only support a single segment.
Also, QEMU is sending a spurious interrupt after the Guest writes to the ERDP register due to the fact that the address written does not match the current index. This is because the index is incremented after sending the event. The xHCI specification states in section 5.5.2.3.3 "When software finishes processing an Event TRB, it will write the address of that Event TRB to the ERDP." Since xhci_write_event() has already incremented the index pointer (intr->er_ep_idx), the check at line 3098 (https://git.qemu.org/?p=qemu.git;a=blob;f=hw/usb/hcd- xhci.c;hb=HEAD#l3090) no longer is valid. I have not studied QEMU's code enough yet to offer a patch. However, this should be a simple fix. intr->er_ep_idx++; if (intr->er_ep_idx >= intr->er_table[intr->er_segment].er_size) { intr->er_ep_idx = 0; intr->er_segment++; if (intr->er_segment >= intr->er_table_size) { intr->er_segment = 0; intr->er_pcs = !intr->er_pcs; } } Being sure to incorporate this new segment member into the above code (possibly as shown) as well as change the lines at 665 to use the new segment member of the structure, and of course in the initialization portion of the event ring. As for the spurious interrupt at line 3101, a new member will need to be added to the code to keep track of the last inserted ED (TRB) into the Event Ring and then of course checking against this new member, not the now newly incremented member. I have sent an email to the author listed at the top of the file as well, not sure if this is proper bug reporting etiquette or not. Thank you. ** Affects: qemu Importance: Undecided Status: New -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1859359 Title: xHCI and event ring handling Status in QEMU: New Bug description: I believe that the Event Ring handling in QEMU is not correct. For example, an Event Ring may have multiple segments. However, the code in xhci_write_event() (https://git.qemu.org/?p=qemu.git;a=blob;f=hw/usb/hcd- xhci.c;hb=HEAD#l645), starting with line 668, seems to only support a single segment. Also, QEMU is sending a spurious interrupt after the Guest writes to the ERDP register due to the fact that the address written does not match the current index. This is because the index is incremented after sending the event. The xHCI specification states in section 5.5.2.3.3 "When software finishes processing an Event TRB, it will write the address of that Event TRB to the ERDP." Since xhci_write_event() has already incremented the index pointer (intr->er_ep_idx), the check at line 3098 (https://git.qemu.org/?p=qemu.git;a=blob;f=hw/usb/hcd- xhci.c;hb=HEAD#l3090) no longer is valid. I have not studied QEMU's code enough yet to offer a patch. However, this should be a simple fix. intr->er_ep_idx++; if (intr->er_ep_idx >= intr->er_table[intr->er_segment].er_size) { intr->er_ep_idx = 0; intr->er_segment++; if (intr->er_segment >= intr->er_table_size) { intr->er_segment = 0; intr->er_pcs = !intr->er_pcs; } } Being sure to incorporate this new segment member into the above code (possibly as shown) as well as change the lines at 665 to use the new segment member of the structure, and of course in the initialization portion of the event ring. As for the spurious interrupt at line 3101, a new member will need to be added to the code to keep track of the last inserted ED (TRB) into the Event Ring and then of course checking against this new member, not the now newly incremented member. I have sent an email to the author listed at the top of the file as well, not sure if this is proper bug reporting etiquette or not. Thank you. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1859359/+subscriptions