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[RFC PATCH 0/3] vfio-pci: Allow to mmap sub-page MMIO BARs and MSI-X table on PPC64 platform

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  [RFC PATCH 0/3] vfio-pci: Allow to mmap sub-page MMIO BARs and MSI-X table on PPC64 platform Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2015-12-11 10:00 +0100
    [RFC PATCH 3/3] vfio-pci: Allow to mmap MSI-X table if EEH is supported Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2015-12-11 10:00 +0100

#1289338 — [RFC PATCH 0/3] vfio-pci: Allow to mmap sub-page MMIO BARs and MSI-X table on PPC64 platform

Current vfio-pci implementation disallows to mmap
sub-page(size < PAGE_SIZE) MMIO BARs and MSI-X table. This is because
sub-page BARs' mmio page may be shared with other BARs and MSI-X table
should not be accessed directly from the guest for security reasons.

But these would cause some performance issues for mmio accesses in guest
when vfio passthrough sub-page BARs or BARs containing MSI-X table on
PPC64 platform. This is because PAGE_SIZE is 64KB by default on PPC64
platform and the big page may easily hit the sub-page MMIO
BARs' unmmapping and cause the unmmaping of the mmio page which
MSI-X table locate in, which lead to mmio emulation in host.

For sub-page MMIO BARs' unmmapping, this patch set enforces all MMIO
BARs to be page aligned on PPC64 platform so that sub-page BAR's mmio
page would not be shared with other BARs. Then we can mmap sub-page
MMIO BARs in vfio-pci driver if all MMIO BARs are page aligned.

For MSI-X table's unmmapping, we think MSI-X table is safe to access
directly from the guest with EEH mechanism enabled which can ensure that
a given pci device can only shoot the MSIs assigned for its PE. So
we add support for mmapping MSI-X table in vfio-pci driver if EEH is
supported.

With this patch set applied, we can get almost 100% improvement on
performance for mmio accesses when we passthrough sub-page BARs in
our test.

The last two patches in the patch set can be used by qemu to:
	- Add support for a VFIO-PCI ioctl to indicate that platform
	  support all PCI BARs are page aligned.
	- Add support for a VFIO-PCI ioctl to indicate that platform
	  support mmapping MSI-X table.

Yongji Xie (3):
  powerpc/pci: Enforce all MMIO BARs to be page aligned
  vfio-pci: Allow to mmap sub-page MMIO BARs if all MMIO BARs are page aligned
  vfio-pci: Allow to mmap MSI-X table if EEH is supported

 arch/powerpc/kernel/pci-common.c    |   10 +++++++++-
 drivers/vfio/pci/vfio_pci.c         |   15 +++++++++++++--
 drivers/vfio/pci/vfio_pci_private.h |   10 ++++++++++
 include/uapi/linux/vfio.h           |    4 ++++
 4 files changed, 36 insertions(+), 3 deletions(-)

-- 
1.7.9.5

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#1289339 — [RFC PATCH 3/3] vfio-pci: Allow to mmap MSI-X table if EEH is supported

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

However, EEH mechanism could ensure that a given pci device
can only shoot the MSIs assigned for its PE and guest kernel also
would not write to MSI-X table in pci_enable_msix() because
para-virtualization on PPC64 platform. So MSI-X table is safe to
access directly from the guest with EEH mechanism enabled.

This patch adds support for this case and allow to mmap MSI-X
table if EEH is supported on PPC64 platform.

And we also add a VFIO_DEVICE_FLAGS_PCI_MSIX_MMAP flag to notify
userspace that it's safe to mmap MSI-X table.

Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
---
 drivers/vfio/pci/vfio_pci.c         |    5 ++++-
 drivers/vfio/pci/vfio_pci_private.h |    5 +++++
 include/uapi/linux/vfio.h           |    2 ++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index dbcad99..85d9980 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -446,6 +446,9 @@ static long vfio_pci_ioctl(void *device_data,
 		if (vfio_pci_bar_page_aligned())
 			info.flags |= VFIO_DEVICE_FLAGS_PCI_PAGE_ALIGNED;
 
+		if (vfio_msix_table_mmap_enabled())
+			info.flags |= VFIO_DEVICE_FLAGS_PCI_MSIX_MMAP;
+
 		info.num_regions = VFIO_PCI_NUM_REGIONS;
 		info.num_irqs = VFIO_PCI_NUM_IRQS;
 
@@ -871,7 +874,7 @@ 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 (index == vdev->msix_bar && !vfio_msix_table_mmap_enabled()) {
 		/*
 		 * Disallow mmaps overlapping the MSI-X table; users don't
 		 * get to touch this directly.  We could find somewhere
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 319352a..835619e 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -74,6 +74,11 @@ static inline bool vfio_pci_bar_page_aligned(void)
 	return IS_ENABLED(CONFIG_PPC64);
 }
 
+static inline bool vfio_msix_table_mmap_enabled(void)
+{
+	return IS_ENABLED(CONFIG_EEH);
+}
+
 extern void vfio_pci_intx_mask(struct vfio_pci_device *vdev);
 extern void vfio_pci_intx_unmask(struct vfio_pci_device *vdev);
 
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 1fc8066..289e662 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -173,6 +173,8 @@ struct vfio_device_info {
 #define VFIO_DEVICE_FLAGS_AMBA  (1 << 3)	/* vfio-amba device */
 /* Platform support all PCI MMIO BARs to be page aligned */
 #define VFIO_DEVICE_FLAGS_PCI_PAGE_ALIGNED	(1 << 4)
+/* Platform support mmapping PCI MSI-X vector table */
+#define VFIO_DEVICE_FLAGS_PCI_MSIX_MMAP	(1 << 5)
 	__u32	num_regions;	/* Max region index + 1 */
 	__u32	num_irqs;	/* Max IRQ index + 1 */
 };
-- 
1.7.9.5

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