Messages in this thread | | | Subject | Re: [PATCH v4] vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive | From | Yongji Xie <> | Date | Thu, 23 Jun 2016 10:39:30 +0800 |
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Hi, Alex
On 2016/6/23 6:04, Alex Williamson wrote:
> On Mon, 30 May 2016 21:06:37 +0800 > Yongji Xie <xyjxie@linux.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@linux.vnet.ibm.com> >> --- > Hi Yongji, > > On 5/22, message-id > <201605230345.u4N3dJip043323@mx0a-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
Thanks, Yongji
>> 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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