[RFC PATCH v2 3/3] vfio-pci: Allow to mmap MSI-X table if EEH is supported

[Yongji Xie <xyjxie@linux.vnet.ibm.com>]

Current vfio-pci implementation disallows to mmap MSI-X
table in case that user get to touch this directly.

However, EEH mechanism can ensure that a given pci device
can only shoot the MSIs assigned for its PE. So we think
it's safe to expose the MSI-X table to userspace because
the exposed MSI-X table can't be used to do harm to other
memory space.

And with MSI-X table mmapped, some performance issues which
are caused when PCI adapters have critical registers in the
same page as the MSI-X table also can be resolved.

So this patch adds a Kconfig option, VFIO_PCI_MMAP_MSIX,
to support for mmapping MSI-X table.

Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
---
 drivers/vfio/pci/Kconfig    |    4 ++++
 drivers/vfio/pci/vfio_pci.c |    6 ++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 02912f1..67b0a2c 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -23,6 +23,10 @@ config VFIO_PCI_MMAP
 	depends on VFIO_PCI
 	def_bool y if !S390
 
+config VFIO_PCI_MMAP_MSIX
+	depends on VFIO_PCI_MMAP
+	def_bool y if EEH
+
 config VFIO_PCI_INTX
 	depends on VFIO_PCI
 	def_bool y if !S390
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 09b3805..d536985 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -555,7 +555,8 @@ static long vfio_pci_ioctl(void *device_data,
 			    IORESOURCE_MEM && (info.size >= PAGE_SIZE ||
 			    pci_resource_page_aligned)) {
 				info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
-				if (info.index == vdev->msix_bar) {
+				if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP_MSIX) &&
+				    info.index == vdev->msix_bar) {
 					ret = msix_sparse_mmap_cap(vdev, &caps);
 					if (ret)
 						return ret;
@@ -967,7 +968,8 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
 	if (phys_len < PAGE_SIZE || req_start + req_len > phys_len)
 		return -EINVAL;
 
-	if (index == vdev->msix_bar) {
+	if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP_MSIX) &&
+	    index == vdev->msix_bar) {
 		/*
 		 * Disallow mmaps overlapping the MSI-X table; users don't
 		 * get to touch this directly.  We could find somewhere
-- 
1.7.9.5