linux-kernel - [PATCH] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected

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Date:   Mon, 30 Jul 2018 16:21:44 -0500
From:   Alexandru Gagniuc <mr.nuke.me@...il.com>
To:     linux-pci@...r.kernel.org, bhelgaas@...gle.com
Cc:     keith.busch@...el.com, alex_gagniuc@...lteam.com,
        austin_bolen@...l.com, shyam_iyer@...l.com, Narendra_K@...l.com,
        Stuart_Hayes@...l.com, lukas@...ner.de,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected

When a PCI device is gone, we don't want to send IO to it if we can
avoid it. We expose functionality via the irq_chip structure. As
users of that structure may not know about the underlying PCI device,
it's our responsibility to guard against removed devices.

irq_write_msi_msg is already guarded. pci_msi_(un)mask_irq are not.
Guard them for completeness.

For example, surprise removal of a PCIe device triggers teardown. This
touches the irq_chips ops some point to disable the interrupts. I/O
generated here can crash the system on machines with buggy firmware.
Not triggering the IO in the first place eliminates the problem.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
---

There's another patch by Lukas Wunner that is needed (not yet published)
in order to fully block IO on SURPRISE!!! removal. The existing code only
sets the PCI_DEV_DISCONNECTED bit in an unreasonably narrow set of
circumstances. Lukas' patch fixes that.

However, this change is otherwise fully independent, and enjoy!

 drivers/pci/msi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 4d88afdfc843..5f47b5cb0401 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -227,6 +227,9 @@ static void msi_set_mask_bit(struct irq_data *data, u32 flag)
 {
 	struct msi_desc *desc = irq_data_get_msi_desc(data);

+	if (pci_dev_is_disconnected(msi_desc_to_pci_dev(desc)))
+		return;
+
 	if (desc->msi_attrib.is_msix) {
 		msix_mask_irq(desc, flag);
 		readl(desc->mask_base);		/* Flush write to device */
-- 
2.17.1