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Date: Thu, 23 Jun 2016 10:39:30 +0800
From: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
To: Alex Williamson <alex.williamson@...hat.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
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
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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