Received-SPF: pass (google.com: domain of linux-kernel+bounces-184932-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: Niklas Schnelle <schnelle@linux.ibm.com>
Date: Tue, 21 May 2024 14:14:57 +0200
Subject: [PATCH 1/3] s390/pci: Fix s390_mmio_read/write syscall page fault
 handling
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Message-Id: <20240521-vfio_pci_mmap-v1-1-2f6315e0054e@linux.ibm.com>
References: <20240521-vfio_pci_mmap-v1-0-2f6315e0054e@linux.ibm.com>
In-Reply-To: <20240521-vfio_pci_mmap-v1-0-2f6315e0054e@linux.ibm.com>
To: Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Gerd Bayer <gbayer@linux.ibm.com>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, Niklas Schnelle <schnelle@linux.ibm.com>

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@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);
+		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