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Message-ID: <20160511151034.GB21753@localhost>
Date: Wed, 11 May 2016 10:10:35 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, alex.williamson@...hat.com,
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 v2] vfio-pci: Allow to mmap sub-page MMIO BARs if the
mmio page is exclusive
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@...ux.vnet.ibm.com>
> ---
> 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)) {
...
> + }
> + if (((res->end + 1) & ~PAGE_MASK)) {
> + /*
> + * Add a dummy resource to reserve the portion
> + * after res->end.
> + */
> + dummy_res2 = kzalloc(sizeof(*dummy_res2), GFP_KERNEL);
> + dummy_res2->resource.start = res->end + 1;
> + dummy_res2->resource.end = (res->start & PAGE_MASK) +
> + PAGE_SIZE - 1;
> + dummy_res2->resource.flags = res->flags;
> + if (request_resource(res->parent,
> + &dummy_res2->resource)) {
> + if (dummy_res1) {
> + list_del(&dummy_res1->res_next);
> + release_resource(&dummy_res1->resource);
> + kfree(dummy_res1);
> + }
> + kfree(dummy_res2);
> + return false;
> + }
> + dummy_res2->index = index;
> + list_add(&dummy_res2->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);
>
> 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 */
> @@ -183,12 +244,17 @@ 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 */
> @@ -217,6 +283,13 @@ 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;
>
> /*
> @@ -587,9 +660,7 @@ 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);
> @@ -1011,16 +1082,16 @@ 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 8a7d546..a4233a8 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;
> @@ -87,6 +94,7 @@ 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
>
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