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    Subject[PATCH 5.10 561/593] vfio/pci: Handle concurrent vma faults
    Date
    From: Alex Williamson <alex.williamson@redhat.com>

    [ Upstream commit 6a45ece4c9af473555f01f0f8b97eba56e3c7d0d ]

    io_remap_pfn_range() will trigger a BUG_ON if it encounters a
    populated pte within the mapping range. This can occur because we map
    the entire vma on fault and multiple faults can be blocked behind the
    vma_lock. This leads to traces like the one reported below.

    We can use our vma_list to test whether a given vma is mapped to avoid
    this issue.

    [ 1591.733256] kernel BUG at mm/memory.c:2177!
    [ 1591.739515] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
    [ 1591.747381] Modules linked in: vfio_iommu_type1 vfio_pci vfio_virqfd vfio pv680_mii(O)
    [ 1591.760536] CPU: 2 PID: 227 Comm: lcore-worker-2 Tainted: G O 5.11.0-rc3+ #1
    [ 1591.770735] Hardware name: , BIOS HixxxxFPGA 1P B600 V121-1
    [ 1591.778872] pstate: 40400009 (nZcv daif +PAN -UAO -TCO BTYPE=--)
    [ 1591.786134] pc : remap_pfn_range+0x214/0x340
    [ 1591.793564] lr : remap_pfn_range+0x1b8/0x340
    [ 1591.799117] sp : ffff80001068bbd0
    [ 1591.803476] x29: ffff80001068bbd0 x28: 0000042eff6f0000
    [ 1591.810404] x27: 0000001100910000 x26: 0000001300910000
    [ 1591.817457] x25: 0068000000000fd3 x24: ffffa92f1338e358
    [ 1591.825144] x23: 0000001140000000 x22: 0000000000000041
    [ 1591.832506] x21: 0000001300910000 x20: ffffa92f141a4000
    [ 1591.839520] x19: 0000001100a00000 x18: 0000000000000000
    [ 1591.846108] x17: 0000000000000000 x16: ffffa92f11844540
    [ 1591.853570] x15: 0000000000000000 x14: 0000000000000000
    [ 1591.860768] x13: fffffc0000000000 x12: 0000000000000880
    [ 1591.868053] x11: ffff0821bf3d01d0 x10: ffff5ef2abd89000
    [ 1591.875932] x9 : ffffa92f12ab0064 x8 : ffffa92f136471c0
    [ 1591.883208] x7 : 0000001140910000 x6 : 0000000200000000
    [ 1591.890177] x5 : 0000000000000001 x4 : 0000000000000001
    [ 1591.896656] x3 : 0000000000000000 x2 : 0168044000000fd3
    [ 1591.903215] x1 : ffff082126261880 x0 : fffffc2084989868
    [ 1591.910234] Call trace:
    [ 1591.914837] remap_pfn_range+0x214/0x340
    [ 1591.921765] vfio_pci_mmap_fault+0xac/0x130 [vfio_pci]
    [ 1591.931200] __do_fault+0x44/0x12c
    [ 1591.937031] handle_mm_fault+0xcc8/0x1230
    [ 1591.942475] do_page_fault+0x16c/0x484
    [ 1591.948635] do_translation_fault+0xbc/0xd8
    [ 1591.954171] do_mem_abort+0x4c/0xc0
    [ 1591.960316] el0_da+0x40/0x80
    [ 1591.965585] el0_sync_handler+0x168/0x1b0
    [ 1591.971608] el0_sync+0x174/0x180
    [ 1591.978312] Code: eb1b027f 540000c0 f9400022 b4fffe02 (d4210000)

    Fixes: 11c4cd07ba11 ("vfio-pci: Fault mmaps to enable vma tracking")
    Reported-by: Zeng Tao <prime.zeng@hisilicon.com>
    Suggested-by: Zeng Tao <prime.zeng@hisilicon.com>
    Link: https://lore.kernel.org/r/162497742783.3883260.3282953006487785034.stgit@omen
    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/vfio/pci/vfio_pci.c | 29 +++++++++++++++++++++--------
    1 file changed, 21 insertions(+), 8 deletions(-)

    diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
    index 48b048edf1ee..57ae8b46b836 100644
    --- a/drivers/vfio/pci/vfio_pci.c
    +++ b/drivers/vfio/pci/vfio_pci.c
    @@ -1614,6 +1614,7 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
    {
    struct vm_area_struct *vma = vmf->vma;
    struct vfio_pci_device *vdev = vma->vm_private_data;
    + struct vfio_pci_mmap_vma *mmap_vma;
    vm_fault_t ret = VM_FAULT_NOPAGE;

    mutex_lock(&vdev->vma_lock);
    @@ -1621,24 +1622,36 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)

    if (!__vfio_pci_memory_enabled(vdev)) {
    ret = VM_FAULT_SIGBUS;
    - mutex_unlock(&vdev->vma_lock);
    goto up_out;
    }

    - if (__vfio_pci_add_vma(vdev, vma)) {
    - ret = VM_FAULT_OOM;
    - mutex_unlock(&vdev->vma_lock);
    - goto up_out;
    + /*
    + * We populate the whole vma on fault, so we need to test whether
    + * the vma has already been mapped, such as for concurrent faults
    + * to the same vma. io_remap_pfn_range() will trigger a BUG_ON if
    + * we ask it to fill the same range again.
    + */
    + list_for_each_entry(mmap_vma, &vdev->vma_list, vma_next) {
    + if (mmap_vma->vma == vma)
    + goto up_out;
    }

    - mutex_unlock(&vdev->vma_lock);
    -
    if (io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
    - vma->vm_end - vma->vm_start, vma->vm_page_prot))
    + vma->vm_end - vma->vm_start,
    + vma->vm_page_prot)) {
    ret = VM_FAULT_SIGBUS;
    + zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start);
    + goto up_out;
    + }
    +
    + if (__vfio_pci_add_vma(vdev, vma)) {
    + ret = VM_FAULT_OOM;
    + zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start);
    + }

    up_out:
    up_read(&vdev->memory_lock);
    + mutex_unlock(&vdev->vma_lock);
    return ret;
    }

    --
    2.30.2


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