[PATCH v3] vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive
From: Yongji Xie
Date: Thu May 12 2016 - 06:21:50 EST
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 a
dummy resource to reserve the remainder of the page which
hot-add device's BAR might be assigned into. But it's not
necessary to handle the case when the BAR is not page aligned.
Because we can't expect the BAR will be assigned into the same
location in a page in guest when we passthrough the BAR. And
it's hard to access this BAR in userspace because we have
no way to get the BAR's location in a page.
Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
---
drivers/vfio/pci/vfio_pci.c | 70 +++++++++++++++++++++++++++++++----
drivers/vfio/pci/vfio_pci_private.h | 8 ++++
2 files changed, 71 insertions(+), 7 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 188b1ff..253c22f 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -110,6 +110,50 @@ 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_res = NULL;
+
+ if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP))
+ return false;
+
+ if (!(res->flags & IORESOURCE_MEM))
+ return false;
+
+ /*
+ * 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)) {
+ /*
+ * Add a dummy resource to reserve the remainder
+ * of the exclusive page in case that hot-add
+ * device's bar is assigned into it.
+ */
+ dummy_res = kzalloc(sizeof(*dummy_res), GFP_KERNEL);
+ if (dummy_res == NULL)
+ return false;
+ dummy_res->resource.start = res->end + 1;
+ dummy_res->resource.end = res->start + PAGE_SIZE - 1;
+ dummy_res->resource.flags = res->flags;
+ if (request_resource(res->parent, &dummy_res->resource)) {
+ kfree(dummy_res);
+ return false;
+ }
+ dummy_res->index = index;
+ list_add(&dummy_res->res_next, &vdev->dummy_resources_list);
+ return true;
+ }
+ return false;
+}
+
static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev);
static void vfio_pci_disable(struct vfio_pci_device *vdev);
@@ -145,10 +189,12 @@ static bool vfio_pci_nointx(struct pci_dev *pdev)
static int vfio_pci_enable(struct vfio_pci_device *vdev)
{
struct pci_dev *pdev = vdev->pdev;
- int ret;
+ int ret, bar;
u16 cmd;
u8 msix_pos;
+ INIT_LIST_HEAD(&vdev->dummy_resources_list);
+
pci_set_power_state(pdev, PCI_D0);
/* Don't allow our initial saved state to include busmaster */
@@ -218,12 +264,17 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
}
}
+ for (bar = PCI_STD_RESOURCES; bar <= PCI_STD_RESOURCE_END; bar++) {
+ vdev->bar_mmap_supported[bar] =
+ vfio_pci_bar_mmap_supported(vdev, bar);
+ }
return 0;
}
static void vfio_pci_disable(struct vfio_pci_device *vdev)
{
struct pci_dev *pdev = vdev->pdev;
+ struct vfio_pci_dummy_resource *dummy_res, *tmp;
int i, bar;
/* Stop the device from further DMA */
@@ -252,6 +303,13 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
vdev->barmap[bar] = NULL;
}
+ list_for_each_entry_safe(dummy_res, tmp,
+ &vdev->dummy_resources_list, res_next) {
+ list_del(&dummy_res->res_next);
+ release_resource(&dummy_res->resource);
+ kfree(dummy_res);
+ }
+
vdev->needs_reset = true;
/*
@@ -623,9 +681,7 @@ static long vfio_pci_ioctl(void *device_data,
info.flags = VFIO_REGION_INFO_FLAG_READ |
VFIO_REGION_INFO_FLAG_WRITE;
- if (IS_ENABLED(CONFIG_VFIO_PCI_MMAP) &&
- pci_resource_flags(pdev, info.index) &
- IORESOURCE_MEM && info.size >= PAGE_SIZE) {
+ if (vdev->bar_mmap_supported[info.index]) {
info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
if (info.index == vdev->msix_bar) {
ret = msix_sparse_mmap_cap(vdev, &caps);
@@ -1049,16 +1105,16 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
return -EINVAL;
if (index >= VFIO_PCI_ROM_REGION_INDEX)
return -EINVAL;
- if (!(pci_resource_flags(pdev, index) & IORESOURCE_MEM))
+ if (!vdev->bar_mmap_supported[index])
return -EINVAL;
- phys_len = pci_resource_len(pdev, index);
+ phys_len = PAGE_ALIGN(pci_resource_len(pdev, index));
req_len = vma->vm_end - vma->vm_start;
pgoff = vma->vm_pgoff &
((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
req_start = pgoff << PAGE_SHIFT;
- if (phys_len < PAGE_SIZE || req_start + req_len > phys_len)
+ if (req_start + req_len > phys_len)
return -EINVAL;
if (index == vdev->msix_bar) {
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 016c14a..2128de8 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -57,9 +57,16 @@ struct vfio_pci_region {
u32 flags;
};
+struct vfio_pci_dummy_resource {
+ struct resource resource;
+ int index;
+ struct list_head res_next;
+};
+
struct vfio_pci_device {
struct pci_dev *pdev;
void __iomem *barmap[PCI_STD_RESOURCE_END + 1];
+ bool bar_mmap_supported[PCI_STD_RESOURCE_END + 1];
u8 *pci_config_map;
u8 *vconfig;
struct perm_bits *msi_perm;
@@ -88,6 +95,7 @@ struct vfio_pci_device {
int refcnt;
struct eventfd_ctx *err_trigger;
struct eventfd_ctx *req_trigger;
+ struct list_head dummy_resources_list;
};
#define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
--
1.7.9.5