linux-kernel - Re: [PATCH v7 1/3] s390/pci: Fix s390_mmio_read/write syscall page fault handling

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Message-ID: <8cff6617-634c-4e10-bd1d-7719edf484ea@linux.ibm.com>
Date: Fri, 28 Feb 2025 16:56:35 -0500
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: Niklas Schnelle <schnelle@...ux.ibm.com>,
        Bjorn Helgaas <helgaas@...nel.org>, Christoph Hellwig <hch@....de>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Thorsten Winkler <twinkler@...ux.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Julian Ruess <julianr@...ux.ibm.com>, Halil Pasic <pasic@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        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>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v7 1/3] s390/pci: Fix s390_mmio_read/write syscall page
 fault handling

On 2/26/25 7:07 AM, Niklas Schnelle wrote:
> 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.
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>