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Date: Fri, 8 Jul 2016 11:15:07 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
bhelgaas@...gle.com, aik@...abs.ru, benh@...nel.crashing.org,
paulus@...ba.org, mpe@...erman.id.au, warrier@...ux.vnet.ibm.com,
zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
gwshan@...ux.vnet.ibm.com, kevin.tian@...el.com
Subject: Re: [PATCH v5] vfio-pci: Allow to mmap sub-page MMIO BARs if the
mmio page is exclusive
On Thu, 30 Jun 2016 15:21:24 +0800
Yongji Xie <xyjxie@...ux.vnet.ibm.com> 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 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@...ux.vnet.ibm.com>
> ---
> drivers/vfio/pci/vfio_pci.c | 88 ++++++++++++++++++++++++++++++++---
> drivers/vfio/pci/vfio_pci_private.h | 8 ++++
> 2 files changed, 90 insertions(+), 6 deletions(-)
Applied to my next branch for v4.8. Thanks,
Alex
>
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 188b1ff..d624a52 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -110,6 +110,74 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
> return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
> }
>
> +static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev)
> +{
> + struct resource *res;
> + int bar;
> + struct vfio_pci_dummy_resource *dummy_res;
> +
> + INIT_LIST_HEAD(&vdev->dummy_resources_list);
> +
> + for (bar = PCI_STD_RESOURCES; bar <= PCI_STD_RESOURCE_END; bar++) {
> + res = vdev->pdev->resource + bar;
> +
> + if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP))
> + goto no_mmap;
> +
> + if (!(res->flags & IORESOURCE_MEM))
> + goto no_mmap;
> +
> + /*
> + * 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))
> + goto no_mmap;
> +
> + if (resource_size(res) >= PAGE_SIZE) {
> + vdev->bar_mmap_supported[bar] = true;
> + continue;
> + }
> +
> + 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)
> + goto no_mmap;
> +
> + dummy_res->resource.name = "vfio sub-page reserved";
> + 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);
> + goto no_mmap;
> + }
> + dummy_res->index = bar;
> + list_add(&dummy_res->res_next,
> + &vdev->dummy_resources_list);
> + vdev->bar_mmap_supported[bar] = true;
> + continue;
> + }
> + /*
> + * Here we don't 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.
> + */
> +no_mmap:
> + vdev->bar_mmap_supported[bar] = false;
> + }
> +}
> +
> static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev);
> static void vfio_pci_disable(struct vfio_pci_device *vdev);
>
> @@ -218,12 +286,15 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
> }
> }
>
> + vfio_pci_probe_mmaps(vdev);
> +
> 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 +323,13 @@ 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 +701,7 @@ 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 +1125,16 @@ 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)
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