Re: [RFC PATCH v5 5/5] vfio-pci: Allow to expose MSI-X table to userspace when safe

David Gibson
2017-08-09T07:00:08Z

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On Mon, Aug 07, 2017 at 05:25:48PM +1000, Alexey Kardashevskiy wrote:
1;4803;0c> Some devices have a MSIX BAR not aligned to the system page size
> greater than 4K (like 64k for ppc64) which at the moment prevents
> such MMIO pages from being mapped to the userspace for the sake of
> the MSIX BAR content protection. If such page happens to share
> the same system page with some frequently accessed registers,
> the entire system page will be emulated which can seriously affect
> performance.
>
> This allows mapping of MSI-X tables to userspace if hardware provides
> MSIX isolation via interrupt remapping or filtering; in other words
> allowing direct access to the MSIX BAR won't do any harm to other devices
> or cause spurious interrupts visible to the kernel.
>
> This adds a wrapping helper to check if a capability is supported by
> an IOMMU group.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> include/linux/vfio.h | 1 +
> drivers/vfio/pci/vfio_pci.c | 20 +++++++++++++++++---
> drivers/vfio/pci/vfio_pci_rdwr.c | 5 ++++-
> drivers/vfio/vfio.c | 15 +++++++++++++++
> 4 files changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 586809abb273..7110bca2fb60 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -46,6 +46,7 @@ struct vfio_device_ops {
>
> extern struct iommu_group *vfio_iommu_group_get(struct device *dev);
> extern void vfio_iommu_group_put(struct iommu_group *group, struct device *dev);
> +extern bool vfio_iommu_group_is_capable(struct device *dev, unsigned long cap);

This diff probably belongs in the earlier patch adding the function,
rather than here where it's first used. Not worth respinning just for
that, though.

> extern int vfio_add_group_dev(struct device *dev,
> const struct vfio_device_ops *ops,
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index d87a0a3cda14..c4c39ed64b1e 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -561,11 +561,17 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> struct vfio_region_info_cap_sparse_mmap *sparse;
> size_t end, size;
> int nr_areas = 2, i = 0, ret;
> + bool is_msix_isolated = vfio_iommu_group_is_capable(&vdev->pdev->dev,
> + IOMMU_GROUP_CAP_ISOLATE_MSIX);
>
> end = pci_resource_len(vdev->pdev, vdev->msix_bar);
>
> - /* If MSI-X table is aligned to the start or end, only one area */
> - if (((vdev->msix_offset & PAGE_MASK) == 0) ||
> + /*
> + * If MSI-X table is allowed to mmap because of the capability
> + * of IRQ remapping or aligned to the start or end, only one area
> + */
> + if (is_msix_isolated ||
> + ((vdev->msix_offset & PAGE_MASK) == 0) ||
> (PAGE_ALIGN(vdev->msix_offset + vdev->msix_size) >= end))
> nr_areas = 1;
>
> @@ -577,6 +583,12 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
>
> sparse->nr_areas = nr_areas;
>
> + if (is_msix_isolated) {
> + sparse->areas[i].offset = 0;
> + sparse->areas[i].size = end;
> + return 0;
> + }
> +
> if (vdev->msix_offset & PAGE_MASK) {
> sparse->areas[i].offset = 0;
> sparse->areas[i].size = vdev->msix_offset & PAGE_MASK;
> @@ -1094,6 +1106,8 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
> unsigned int index;
> u64 phys_len, req_len, pgoff, req_start;
> int ret;
> + bool is_msix_isolated = vfio_iommu_group_is_capable(&vdev->pdev->dev,
> + IOMMU_GROUP_CAP_ISOLATE_MSIX);
>
> index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
>
> @@ -1115,7 +1129,7 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
> if (req_start + req_len > phys_len)
> return -EINVAL;
>
> - if (index == vdev->msix_bar) {
> + if (index == vdev->msix_bar && !is_msix_isolated) {
> /*
> * Disallow mmaps overlapping the MSI-X table; users don't
> * get to touch this directly. We could find somewhere
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index 357243d76f10..7514206a5ea7 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -18,6 +18,7 @@
> #include <linux/uaccess.h>
> #include <linux/io.h>
> #include <linux/vgaarb.h>
> +#include <linux/vfio.h>
>
> #include "vfio_pci_private.h"
>
> @@ -123,6 +124,8 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
> resource_size_t end;
> void __iomem *io;
> ssize_t done;
> + bool is_msix_isolated = vfio_iommu_group_is_capable(&vdev->pdev->dev,
> + IOMMU_GROUP_CAP_ISOLATE_MSIX);
>
> if (pci_resource_start(pdev, bar))
> end = pci_resource_len(pdev, bar);
> @@ -164,7 +167,7 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
> } else
> io = vdev->barmap[bar];
>
> - if (bar == vdev->msix_bar) {
> + if (bar == vdev->msix_bar && !is_msix_isolated) {
> x_start = vdev->msix_offset;
> x_end = vdev->msix_offset + vdev->msix_size;
> }
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 330d50582f40..5292c4a5ae8f 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -169,6 +169,21 @@ void vfio_iommu_group_put(struct iommu_group *group, struct device *dev)
> }
> EXPORT_SYMBOL_GPL(vfio_iommu_group_put);
>
> +bool vfio_iommu_group_is_capable(struct device *dev, unsigned long cap)
> +{
> + bool ret = false;
> + struct iommu_group *group = vfio_iommu_group_get(dev);
> +
> + if (group) {
> + ret = iommu_group_is_capable(group, cap);
> +
> + vfio_iommu_group_put(group, dev);
> + }
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(vfio_iommu_group_is_capable);
> +
> #ifdef CONFIG_VFIO_NOIOMMU
> static void *vfio_noiommu_open(unsigned long arg)
> {

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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