From 93623a848fba7757a0840b78d7b3874bab4d7a1b Mon Sep 17 00:00:00 2001
From: John Snow <jsnow@redhat.com>
Date: Tue, 10 Jul 2018 23:06:15 +0200
Subject: [PATCH 206/268] ahci: fix PxCI register race
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RH-Author: John Snow <jsnow@redhat.com>
Message-id: <20180710230616.11000-3-jsnow@redhat.com>
Patchwork-id: 81293
O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 2/3] ahci: fix PxCI register race
Bugzilla: 1584914
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Fixes: https://bugs.launchpad.net/qemu/+bug/1769189

AHCI presently signals completion prior to the PxCI register being
cleared to indicate completion. If a guest driver attempts to issue
a new command in its IRQ handler, it might be surprised to learn there
is still a command pending.

In the case of Windows 10's boot driver, it will actually poll the IRQ
register hoping to find out when the command is done running -- which
will never happen, as there isn't a command running.

Fix this: clear PxCI in ahci_cmd_done and not in the asynchronous BH.
Because it now runs synchronously, we don't need to check if the command
is actually done by spying on the ATA registers. We know it's done.

CC: qemu-stable <qemu-stable@nongnu.org>
Reported-by: François Guerraz <kubrick@fgv6.net>
Tested-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Message-id: 20180531004323.4611-3-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
(cherry picked from commit 5694c7eacce6b263ad7497cc1bb76aad746cfd4e)
Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/ide/ahci.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index b7a6f68..a9558e4 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -532,13 +532,6 @@ static void ahci_check_cmd_bh(void *opaque)
     qemu_bh_delete(ad->check_bh);
     ad->check_bh = NULL;
 
-    if ((ad->busy_slot != -1) &&
-        !(ad->port.ifs[0].status & (BUSY_STAT|DRQ_STAT))) {
-        /* no longer busy */
-        ad->port_regs.cmd_issue &= ~(1 << ad->busy_slot);
-        ad->busy_slot = -1;
-    }
-
     check_cmd(ad->hba, ad->port_no);
 }
 
@@ -1425,6 +1418,12 @@ static void ahci_cmd_done(IDEDMA *dma)
 
     trace_ahci_cmd_done(ad->hba, ad->port_no);
 
+    /* no longer busy */
+    if (ad->busy_slot != -1) {
+        ad->port_regs.cmd_issue &= ~(1 << ad->busy_slot);
+        ad->busy_slot = -1;
+    }
+
     /* update d2h status */
     ahci_write_fis_d2h(ad);
 
-- 
1.8.3.1