| Message ID | 20240523-vfio_pci_mmap-v2-1-0dc6c139a4f1@linux.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | vfio/pci: s390: Fix issues preventing VFIO_PCI_MMAP=y for s390 and enable it | expand |
On Thu, 2024-05-23 at 13:10 +0200, Niklas Schnelle wrote: > The s390 MMIO syscalls when using the classic PCI instructions do not > cause a page fault when follow_pte() fails due to the page not being > present. Besides being a general deficiency this breaks vfio-pci's mmap() > handling once VFIO_PCI_MMAP gets enabled as this lazily maps on first > access. Fix this by following a failed follow_pte() with > fixup_user_page() and retrying the follow_pte(). > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> > --- > arch/s390/pci/pci_mmio.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c > index a90499c087f0..217defbcb4f1 100644 > --- a/arch/s390/pci/pci_mmio.c > +++ b/arch/s390/pci/pci_mmio.c > @@ -170,8 +170,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, > goto out_unlock_mmap; > > ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); > - if (ret) > - goto out_unlock_mmap; > + if (ret) { > + fixup_user_fault(vma->vm_mm, mmio_addr, FAULT_FLAG_WRITE, NULL); > + ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); This needs a slight adjustment in v6.10-rc1 due to a change in follow_pte()'s signature. The above should take "vma" directly. We could then also use current->mm in fixup_user_fault() as seems more common. I've already pushed this to my kernel.org repository and will send a v3 rebased on v6.10-rc1 with just this as I'm not tracking any other feedback. > + if (ret) > + goto out_unlock_mmap; > + } > > io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | > (mmio_addr & ~PAGE_MASK)); > @@ -305,12 +309,16 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr, > if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) > goto out_unlock_mmap; > ret = -EACCES; > - if (!(vma->vm_flags & VM_WRITE)) > + if (!(vma->vm_flags & VM_READ)) > goto out_unlock_mmap; > > ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); > - if (ret) > - goto out_unlock_mmap; > + if (ret) { > + fixup_user_fault(vma->vm_mm, mmio_addr, 0, NULL); > + ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); Here as well > + if (ret) > + goto out_unlock_mmap; > + } > > io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | > (mmio_addr & ~PAGE_MASK)); >
On 5/23/24 7:10 AM, Niklas Schnelle wrote: > The s390 MMIO syscalls when using the classic PCI instructions do not > cause a page fault when follow_pte() fails due to the page not being > present. Besides being a general deficiency this breaks vfio-pci's mmap() > handling once VFIO_PCI_MMAP gets enabled as this lazily maps on first > access. Fix this by following a failed follow_pte() with > fixup_user_page() and retrying the follow_pte(). > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com> FYI, as of -rc1 this patch has a merge conflict with 29ae7d96d166 ("mm: pass VMA instead of MM to follow_pte().")
diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c index a90499c087f0..217defbcb4f1 100644 --- a/arch/s390/pci/pci_mmio.c +++ b/arch/s390/pci/pci_mmio.c @@ -170,8 +170,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, goto out_unlock_mmap; ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); - if (ret) - goto out_unlock_mmap; + if (ret) { + fixup_user_fault(vma->vm_mm, mmio_addr, FAULT_FLAG_WRITE, NULL); + ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); + if (ret) + goto out_unlock_mmap; + } io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | (mmio_addr & ~PAGE_MASK)); @@ -305,12 +309,16 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr, if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) goto out_unlock_mmap; ret = -EACCES; - if (!(vma->vm_flags & VM_WRITE)) + if (!(vma->vm_flags & VM_READ)) goto out_unlock_mmap; ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); - if (ret) - goto out_unlock_mmap; + if (ret) { + fixup_user_fault(vma->vm_mm, mmio_addr, 0, NULL); + ret = follow_pte(vma->vm_mm, mmio_addr, &ptep, &ptl); + if (ret) + goto out_unlock_mmap; + } io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | (mmio_addr & ~PAGE_MASK));