On 2016/5/11 23:10, Bjorn Helgaas wrote:
On Wed, May 11, 2016 at 07:34:19PM +0800, Yongji Xie wrote:
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. This will cause some
performance issues when we passthrough a PCI device with
this kind of BARs. Guest will be not able to handle the mmio
accesses to the BARs which leads to mmio emulations in host.
However, not all sub-page BARs will share page with other BARs.
We should allow to mmap the sub-page MMIO BARs which we can
make sure will not share page with other BARs.
This patch adds support for this case. And we try to add some
dummy resources to reserve the remaind of the page which
hot-add device's BAR might be assigned into.
This is starting to look more reasonable from a safety perspective.
At least I don't have an allergic reaction to mapping a page that may
contain BARs from other random devices :)
Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
---
drivers/vfio/pci/vfio_pci.c | 85 ++++++++++++++++++++++++++++++++---
drivers/vfio/pci/vfio_pci_private.h | 8 ++++
2 files changed, 86 insertions(+), 7 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 98059df..33282b8 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -110,16 +110,77 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
}
+static bool vfio_pci_bar_mmap_supported(struct vfio_pci_device *vdev, int index)
+{
+ struct resource *res = vdev->pdev->resource + index;
+ struct vfio_pci_dummy_resource *dummy_res1 = NULL;
+ struct vfio_pci_dummy_resource *dummy_res2 = NULL;
+
+ if (IS_ENABLED(CONFIG_VFIO_PCI_MMAP) && res->flags & IORESOURCE_MEM &&
+ resource_size(res) > 0) {
+ if (resource_size(res) >= PAGE_SIZE)
+ return true;
+
+ if ((res->start & ~PAGE_MASK)) {
+ /*
+ * Add a dummy resource to reserve the portion
+ * before res->start in exclusive page in case
+ * that hot-add device's bar is assigned into it.
+ */
+ dummy_res1 = kzalloc(sizeof(*dummy_res1), GFP_KERNEL);
Should check for kzalloc() failure here.
+ dummy_res1->resource.start = res->start & PAGE_MASK;
+ dummy_res1->resource.end = res->start - 1;
+ dummy_res1->resource.flags = res->flags;
+ if (request_resource(res->parent,
+ &dummy_res1->resource)) {
+ kfree(dummy_res1);
+ return false;
+ }
+ dummy_res1->index = index;
+ list_add(&dummy_res1->res_next,
+ &vdev->dummy_resources_list);
The main body of this function is unnecessarily indented. If you did
this it would be less indented:
if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP))
return false;
if (!res->flags & IORESOURCE_MEM)
return false;
/*
* Not sure this is necessary; the PCI core *shouldn't* set up a
* resource with a type but zero size. But there may be bugs that
* cause us to do that.
*/
if (!resource_size(res))
return false;
if (resource_size(res) >= PAGE_SIZE)
return true;
if ((res->start & ~PAGE_MASK)) {
...
Thanks for your comments. I'll send a v3 soon.
Regards,
Yongji
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
