linux-kernel - Re: [PATCH v2 1/3] s390/pci: Fix s390_mmio_read/write syscall page fault handling

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Date: Tue, 28 May 2024 11:13:09 -0400
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: Niklas Schnelle <schnelle@...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>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v2 1/3] s390/pci: Fix s390_mmio_read/write syscall page
 fault handling

On 5/23/24 7:10 AM, Niklas Schnelle wrote:
> 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().
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

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

FYI, as of -rc1 this patch has a merge conflict with 29ae7d96d166 ("mm: pass VMA instead of MM to follow_pte().")