mmap/munmap in sysfs

From: Bjorn Helgaas
Date: Tue Jun 25 2019 - 18:36:12 EST

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);