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Blame 0130-usb-ehci-Drop-cached-qhs-when-the-doorbell-gets-rung.patch

Hans de Goede 1b1995
From 35562fb521547e081e732453a6395fc00d9ee9e4 Mon Sep 17 00:00:00 2001
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From: Hans de Goede <hdegoede@redhat.com>
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Date: Thu, 1 Mar 2012 15:20:17 +0100
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Subject: [PATCH 130/140] usb-ehci: Drop cached qhs when the doorbell gets
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 rung
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The purpose of the IAAD bit / the doorbell is to make the ehci controller
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forget about cached qhs, this is mainly used when cancelling transactions,
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the qh is unlinked from the async schedule and then the doorbell gets rung,
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once the doorbell is acked by the controller the hcd knows that the qh is
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no longer in use and that it can do something else with the memory, such
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as re-use it for a new qh! But we keep our struct representing this qh around
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for circa 250 ms. This allows for a (mightily large) race window where the
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following could happen:
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-hcd submits a qh at address 0xdeadbeef
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-our ehci code sees the qh, sends a request to a usb-device, gets a result
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 of USB_RET_ASYNC, sets the async_state of the qh to EHCI_ASYNC_INFLIGHT
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-hcd unlinks the qh at address 0xdeadbeef
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-hcd rings the doorbell, wait for us to ack it
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-hcd re-uses the qh at address 0xdeadbeef
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-our ehci code sees the qh, looks in the async_queue, sees there already is
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 a qh at address 0xdeadbeef there with async_state of EHCI_ASYNC_INFLIGHT,
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 does nothing
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-the *original* (which the hcd thinks it has cancelled) transaction finishes
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-our ehci code sees the qh on yet another pass through the async list,
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 looks in the async_queue, sees there already is a qh at address 0xdeadbeef
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 there with async_state of EHCI_ASYNC_COMPLETED, and finished the transaction
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 with the results of the *original* transaction.
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Not good (tm), this patch fixes this race by removing all qhs which have not
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been seen during the last cycle through the async list immidiately when the
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doorbell is rung.
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Note this patch does not fix any actually observed problem, but upon
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reading of the EHCI spec it became apparent to me that the above race could
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happen and the usb-ehci behavior from before this patch is not good.
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Signed-off-by: Hans de Goede <hdegoede@redhat.com>
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---
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 hw/usb-ehci.c |   31 ++++++++++++++++---------------
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 1 file changed, 16 insertions(+), 15 deletions(-)
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diff --git a/hw/usb-ehci.c b/hw/usb-ehci.c
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index 422afc8..b8ba483 100644
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--- a/hw/usb-ehci.c
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+++ b/hw/usb-ehci.c
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@@ -697,7 +697,7 @@ static EHCIQueue *ehci_find_queue_by_qh(EHCIState *ehci, uint32_t addr,
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     return NULL;
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 }
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-static void ehci_queues_rip_unused(EHCIState *ehci, int async)
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+static void ehci_queues_rip_unused(EHCIState *ehci, int async, int flush)
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 {
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     EHCIQueueHead *head = async ? &ehci->aqueues : &ehci->pqueues;
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     EHCIQueue *q, *tmp;
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@@ -708,7 +708,7 @@ static void ehci_queues_rip_unused(EHCIState *ehci, int async)
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             q->ts = ehci->last_run_ns;
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             continue;
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         }
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-        if (ehci->last_run_ns < q->ts + 250000000) {
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+        if (!flush && ehci->last_run_ns < q->ts + 250000000) {
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             /* allow 0.25 sec idle */
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             continue;
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         }
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@@ -1565,7 +1565,7 @@ static int ehci_state_waitlisthead(EHCIState *ehci,  int async)
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         ehci_set_usbsts(ehci, USBSTS_REC);
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     }
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-    ehci_queues_rip_unused(ehci, async);
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+    ehci_queues_rip_unused(ehci, async, 0);
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     /*  Find the head of the list (4.9.1.1) */
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     for(i = 0; i < MAX_QH; i++) {
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@@ -2121,18 +2121,7 @@ static void ehci_advance_async_state(EHCIState *ehci)
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             break;
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         }
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-        /* If the doorbell is set, the guest wants to make a change to the
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-         * schedule. The host controller needs to release cached data.
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-         * (section 4.8.2)
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-         */
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-        if (ehci->usbcmd & USBCMD_IAAD) {
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-            DPRINTF("ASYNC: doorbell request acknowledged\n");
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-            ehci->usbcmd &= ~USBCMD_IAAD;
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-            ehci_set_interrupt(ehci, USBSTS_IAA);
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-            break;
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-        }
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-
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-        /* make sure guest has acknowledged */
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+        /* make sure guest has acknowledged the doorbell interrupt */
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         /* TO-DO: is this really needed? */
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         if (ehci->usbsts & USBSTS_IAA) {
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             DPRINTF("IAA status bit still set.\n");
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@@ -2146,6 +2135,18 @@ static void ehci_advance_async_state(EHCIState *ehci)
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         ehci_set_state(ehci, async, EST_WAITLISTHEAD);
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         ehci_advance_state(ehci, async);
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+
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+        /* If the doorbell is set, the guest wants to make a change to the
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+         * schedule. The host controller needs to release cached data.
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+         * (section 4.8.2)
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+         */
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+        if (ehci->usbcmd & USBCMD_IAAD) {
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+            /* Remove all unseen qhs from the async qhs queue */
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+            ehci_queues_rip_unused(ehci, async, 1);
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+            DPRINTF("ASYNC: doorbell request acknowledged\n");
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+            ehci->usbcmd &= ~USBCMD_IAAD;
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+            ehci_set_interrupt(ehci, USBSTS_IAA);
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+        }
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         break;
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     default:
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-- 
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1.7.9.3
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