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Date: Wed, 22 Jun 2016 20:54:54 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...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 v4] vfio-pci: Allow to mmap sub-page MMIO BARs if the
mmio page is exclusive
On Thu, 23 Jun 2016 10:39:30 +0800
Yongji Xie <xyjxie@...ux.vnet.ibm.com> wrote:
> Hi, Alex
>
> On 2016/6/23 6:04, Alex Williamson wrote:
>
> > On Mon, 30 May 2016 21:06:37 +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>
> >> ---
> > Hi Yongji,
> >
> > On 5/22, message-id
> > <201605230345.u4N3dJip043323@...a-001b2d01.pphosted.com> you indicated
> > you'd post the QEMU code which is enabled by this patch "soon". Have I
> > missed that? I'm still waiting to see it. Thanks,
> >
> > Alex
>
> I posted it on May 24th [1]. Do I need to resend it?
>
> [1] http://lists.nongnu.org/archive/html/qemu-devel/2016-05/msg04125.html
I found it. Thanks,
Alex
> >> drivers/vfio/pci/vfio_pci.c | 87 ++++++++++++++++++++++++++++++++---
> >> drivers/vfio/pci/vfio_pci_private.h | 8 ++++
> >> 2 files changed, 89 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index 188b1ff..3cca2a7 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -110,6 +110,73 @@ 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.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 +285,15 @@ 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 +322,13 @@ 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 +700,7 @@ 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 +1124,16 @@ 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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