On 2015/12/18 5:46, Alex Williamson wrote:

On Thu, 2015-12-17 at 18:26 +0800, yongji xie wrote:

quoted

On 2015/12/17 4:04, Alex Williamson wrote:

quoted

On Fri, 2015-12-11 at 16:53 +0800, Yongji Xie wrote:

quoted

Current vfio-pci implementation disallows to mmap
sub-page(size < PAGE_SIZE) MMIO BARs because these BARs' mmio
page
may be shared with other BARs.

But we should allow to mmap these sub-page MMIO BARs if all MMIO
BARs
are page aligned which leads the BARs' mmio page would not be
shared
with other BARs.

This patch adds support for this case and we also add a
VFIO_DEVICE_FLAGS_PCI_PAGE_ALIGNED flag to notify userspace that
platform supports all MMIO BARs to be page aligned.

Signed-off-by: Yongji Xie <redacted>
---
   drivers/vfio/pci/vfio_pci.c         |   10 +++++++++-
   drivers/vfio/pci/vfio_pci_private.h |    5 +++++
   include/uapi/linux/vfio.h           |    2 ++
   3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci.c

b/drivers/vfio/pci/vfio_pci.c
index 32b88bd..dbcad99 100644

--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c

@@ -443,6 +443,9 @@ static long vfio_pci_ioctl(void *device_data,
   		if (vdev->reset_works)
   			info.flags |= VFIO_DEVICE_FLAGS_RESET;
   
+		if (vfio_pci_bar_page_aligned())
+			info.flags |=

VFIO_DEVICE_FLAGS_PCI_PAGE_ALIGNED;
+
   		info.num_regions = VFIO_PCI_NUM_REGIONS;
   		info.num_irqs = VFIO_PCI_NUM_IRQS;
   

@@ -479,7 +482,8 @@ static long vfio_pci_ioctl(void *device_data,
   				     VFIO_REGION_INFO_FLAG_WRIT

E;
   			if (IS_ENABLED(CONFIG_VFIO_PCI_MMAP) &&
   			    pci_resource_flags(pdev,
info.index) &
-			    IORESOURCE_MEM && info.size >=
PAGE_SIZE)
+			    IORESOURCE_MEM && (info.size >=
PAGE_SIZE ||
+			    vfio_pci_bar_page_aligned()))
   				info.flags |=
VFIO_REGION_INFO_FLAG_MMAP;
   			break;
   		case VFIO_PCI_ROM_REGION_INDEX:

@@ -855,6 +859,10 @@ static int vfio_pci_mmap(void *device_data,

struct vm_area_struct *vma)
   		return -EINVAL;
   
   	phys_len = pci_resource_len(pdev, index);
+
+	if (vfio_pci_bar_page_aligned())
+		phys_len = PAGE_ALIGN(phys_len);
+
   	req_len = vma->vm_end - vma->vm_start;
   	pgoff = vma->vm_pgoff &
   		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) -
1);

diff --git a/drivers/vfio/pci/vfio_pci_private.h

b/drivers/vfio/pci/vfio_pci_private.h
index 0e7394f..319352a 100644

--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h

@@ -69,6 +69,11 @@ struct vfio_pci_device {
   #define is_irq_none(vdev) (!(is_intx(vdev) || is_msi(vdev) ||

is_msix(vdev)))
   #define irq_is(vdev, type) (vdev->irq_type == type)
   
+static inline bool vfio_pci_bar_page_aligned(void)
+{
+	return IS_ENABLED(CONFIG_PPC64);
+}

I really dislike this.  This is a problem for any architecture that
runs on larger pages, and even an annoyance on 4k hosts.  Why are
we
only solving it for PPC64?

Yes, I know it's a problem for other architectures. But I'm not sure
if
other archs prefer
to enforce the alignment of all BARs to be at least PAGE_SIZE which
would result in
some waste of address space.

So I just propose a prototype and add PPC64 support here. And other
archs could decide
to use it or not by themselves.

quoted

Can't we do something similar in the core PCI code and detect it?

So you mean we can do it like this:

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index d390fc1..f46c04d 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h

@@ -320,6 +320,11 @@ static inline resource_size_t

pci_resource_alignment(struct pci_dev *dev,
          return resource_alignment(res);
   }

+static inline bool pci_bar_page_aligned(void)
+{
+       return IS_ENABLED(CONFIG_PPC64);
+}
+
   void pci_enable_acs(struct pci_dev *dev);

   struct pci_dev_reset_methods {

or add a config option to indicate that PCI MMIO BARs should be page
aligned?

Yes, I'm thinking of a boot commandline option, maybe one that PPC64
can default to enabled if it chooses to.  The problem is not unique to
PPC64 and the solution should not be unique either.  I don't want to
need to revisit this for ARM, which we know is going to be similarly
afflicted.  Thanks,

Alex

OK. I will try to fix it by adding a boot commandline option.
It seems to be better than adding a config option. Thanks

Regards
Yongji Xie