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s390/pci: Fix s390_mmio_read/write syscall page fault handling

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The s390 MMIO syscalls when using the classic PCI instructions do not
cause a page fault when follow_pfnmap_start() 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_pfnmap_start() with
fixup_user_page() and retrying the follow_pfnmap_start(). Also fix
a VM_READ vs VM_WRITE mixup in the read syscall.

Link: https://lore.kernel.org/r/20250226-vfio_pci_mmap-v7-1-c5c0f1d26efd@linux.ibm.com
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
This commit is contained in:
Niklas Schnelle 2025-02-26 13:07:45 +01:00 committed by Bjorn Helgaas
parent 04d50d953a
commit 41a0926e82
1 changed files with 13 additions and 5 deletions
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18
arch/s390/pci/pci_mmio.c
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@ -175,8 +175,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
args.address = mmio_addr;
args.vma = vma;
ret = follow_pfnmap_start(&args);
if (ret)
goto out_unlock_mmap;
if (ret) {
fixup_user_fault(current->mm, mmio_addr, FAULT_FLAG_WRITE, NULL);
ret = follow_pfnmap_start(&args);
if (ret)
goto out_unlock_mmap;
}
io_addr = (void __iomem *)((args.pfn << PAGE_SHIFT) |
(mmio_addr & ~PAGE_MASK));
@ -315,14 +319,18 @@ 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;
args.vma = vma;
args.address = mmio_addr;
ret = follow_pfnmap_start(&args);
if (ret)
goto out_unlock_mmap;
if (ret) {
fixup_user_fault(current->mm, mmio_addr, 0, NULL);
ret = follow_pfnmap_start(&args);
if (ret)
goto out_unlock_mmap;
}
io_addr = (void __iomem *)((args.pfn << PAGE_SHIFT) |
(mmio_addr & ~PAGE_MASK));