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Date: Wed, 22 May 2024 20:18:52 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: 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>, linux-s390@vger.kernel.org,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 1/3] s390/pci: Fix s390_mmio_read/write syscall page
 fault handling
Message-ID: <20240522231852.GF69273@ziepe.ca>
References: <20240521-vfio_pci_mmap-v1-0-2f6315e0054e@linux.ibm.com>
 <20240521-vfio_pci_mmap-v1-1-2f6315e0054e@linux.ibm.com>
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In-Reply-To: <20240521-vfio_pci_mmap-v1-1-2f6315e0054e@linux.ibm.com>

On Tue, May 21, 2024 at 02:14:57PM +0200, 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().
> 
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
>  arch/s390/pci/pci_mmio.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason