6.14-stable review patch. If anyone has any objections, please let me know.
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From: Niklas Schnelle schnelle@linux.ibm.com
[ Upstream commit 41a0926e82f4963046876ed9a1b5f681be8087a8 ]
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... 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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 46f99dc164ade..1997d9b7965df 100644 --- a/arch/s390/pci/pci_mmio.c +++ b/arch/s390/pci/pci_mmio.c @@ -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));