linux-kernel - mmap/munmap in sysfs

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Date:   Tue, 25 Jun 2019 17:36:08 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Myron Stowe <myron.stowe@...hat.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: mmap/munmap in sysfs

Hi Greg, et al,

Userspace can mmap PCI device memory via the resourceN files in sysfs,
which use pci_mmap_resource().  I think this path is unaware of power
management, so the device may be runtime-suspended, e.g., it may be in
D1, D2, or D3, where it will not respond to memory accesses.

Userspace accesses while the device is suspended will cause PCI
errors, so I think we need something like the patch below.  But this
isn't sufficient by itself because we would need a corresponding
pm_runtime_put() when the mapping goes away.  Where should that go?
Or is there a better way to do this?

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 6d27475e39b2..aab7a47679a7 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1173,6 +1173,7 @@ static int pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,

 	mmap_type = res->flags & IORESOURCE_MEM ? pci_mmap_mem : pci_mmap_io;

+	pm_runtime_get_sync(pdev);
 	return pci_mmap_resource_range(pdev, bar, vma, mmap_type, write_combine);
 }