linux-kernel - [PATCH RFC v2 3/4] PCI: hotplug: Wait for PDS when in-band presence is disabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:   Tue, 19 Feb 2019 19:20:29 -0600
From:   Alexandru Gagniuc <mr.nuke.me@...il.com>
To:     bhelgaas@...gle.com
Cc:     austin_bolen@...l.com, alex_gagniuc@...lteam.com,
        keith.busch@...el.com, Shyam_Iyer@...l.com, lukas@...ner.de,
        okaya@...nel.org, linux-pci@...r.kernel.org,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Oza Pawandeep <poza@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH RFC v2 3/4] PCI: hotplug: Wait for PDS when in-band presence is disabled

When inband presence is disabled, PDS may come up at any time, or not
at all. PDS being low may indicate that the card is still mating, and
we could expect contact bounce to bring down the link as well.

It is reasonable to assume that most cards will mate in a hotplug slot
in less than a second. Thus, when we know PDS only reflects
out-of-band presence, it's worthwhile to wait the extra second and
make sure the card is properly mated before loading the driver.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
---
 drivers/pci/hotplug/pciehp_hpc.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index f77dc7c38f9a..9bcadb5d3561 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -240,6 +240,25 @@ static bool pci_bus_check_dev(struct pci_bus *bus, int devfn)
 	return found;
 }
 
+static void pcie_wait_for_presence(struct pci_dev *pdev)
+{
+	int timeout = 1000;
+	bool pds;
+	u16 slot_status;
+
+	while (true) {
+		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
+		pds = !!(slot_status & PCI_EXP_SLTSTA_PDS);
+		if (pds || timeout <= 0)
+			break;
+		msleep(20);
+		timeout -= 20;
+	}
+
+	if (!pds)
+		pci_info(pdev, "Presence Detect state not set in 1000 msec\n");
+}
+
 int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
@@ -249,6 +268,9 @@ int pciehp_check_link_status(struct controller *ctrl)
 	if (!pcie_wait_for_link(pdev, true))
 		return -1;
 
+	if (ctrl->inband_presence_disabled)
+		pcie_wait_for_presence(pdev);
+
 	found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
 					PCI_DEVFN(0, 0));
 
-- 
2.19.2