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Message-Id: <20240521-vfio_pci_mmap-v1-1-2f6315e0054e@linux.ibm.com>
Date: Tue, 21 May 2024 14:14:57 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Alex Williamson <alex.williamson@...hat.com>,
Gerd Bayer <gbayer@...ux.ibm.com>,
Matthew Rosato <mjrosato@...ux.ibm.com>,
Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: [PATCH 1/3] s390/pci: Fix s390_mmio_read/write syscall page fault
handling
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().
Signed-off-by: Niklas Schnelle <schnelle@...ux.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);
+ 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));
--
2.40.1
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