svn commit: r348681 - head/sys/dev/pci

[Colin Percival]

Author: cperciva
Date: Wed Jun  5 04:58:42 2019
New Revision: 348681
URL: https://svnweb.freebsd.org/changeset/base/348681

Log:
  Only respond to the PCIe Attention Button if a device is already plugged in.
  
  Prior to this commit, if PCIEM_SLOT_STA_ABP and PCIEM_SLOT_STA_PDC are
  asserted simultaneously, FreeBSD sets a 5 second "hardware going away" timer
  and then processes the "presence detect" change. In the (physically
  challenging) case that someone presses the "attention button" and inserts
  a new PCIe device at exactly the same moment, this results in FreeBSD
  recognizing that the device is present, attaching it, and then detaching it
  5 seconds later.
  
  On EC2 "bare metal" hardware this is the precise sequence of events which
  takes place when a new EBS volume is attached; virtual machines have no
  difficulty effecting physically implausible simultaneity.
  
  This patch changes the handling of PCIEM_SLOT_STA_ABP to only detach a
  device if the presence of a device was detected *before* the interrupt
  which reports the Attention Button push.
  
  Reported by:	Matt Wilson
  Reviewed by:	jhb
  MFC after:	1 week
  Sponsored by:	https://www.patreon.com/cperciva
  Differential Revision:	https://reviews.freebsd.org/D20499

Modified:
  head/sys/dev/pci/pci_pci.c

Modified: head/sys/dev/pci/pci_pci.c
==============================================================================
--- head/sys/dev/pci/pci_pci.c	Wed Jun  5 04:01:31 2019	(r348680)
+++ head/sys/dev/pci/pci_pci.c	Wed Jun  5 04:58:42 2019	(r348681)
@@ -1170,9 +1170,11 @@ pcib_pcie_intr_hotplug(void *arg)
 {
 	struct pcib_softc *sc;
 	device_t dev;
+	uint16_t old_slot_sta;
 
 	sc = arg;
 	dev = sc->dev;
+	old_slot_sta = sc->pcie_slot_sta;
 	sc->pcie_slot_sta = pcie_read_config(dev, PCIER_SLOT_STA, 2);
 
 	/* Clear the events just reported. */
@@ -1188,7 +1190,8 @@ pcib_pcie_intr_hotplug(void *arg)
 			    "Attention Button Pressed: Detach Cancelled\n");
 			sc->flags &= ~PCIB_DETACH_PENDING;
 			callout_stop(&sc->pcie_ab_timer);
-		} else {
+		} else if (old_slot_sta & PCIEM_SLOT_STA_PDS) {
+			/* Only initiate detach sequence if device present. */
 			device_printf(dev,
 		    "Attention Button Pressed: Detaching in 5 seconds\n");
 			sc->flags |= PCIB_DETACH_PENDING;