linux-kernel - Re: [PATCH] vfio/pci: take mmap write lock for io_remap_pfn

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Message-ID: <ZF0qRLtteE4mtRdT@nvidia.com>
Date:   Thu, 11 May 2023 14:47:48 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Yan Zhao <yan.y.zhao@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kevin.tian@...el.com,
        yishaih@...dia.com, shameerali.kolothum.thodi@...wei.com,
        Cédric Le Goater <clg@...hat.com>
Subject: Re: [PATCH] vfio/pci: take mmap write lock for io_remap_pfn_range

On Thu, May 11, 2023 at 10:07:06AM -0600, Alex Williamson wrote:

> > I vaugely remember the address_space conversion might help remove the
> > fault handler?
> 
> Yes, this did remove the fault handler entirely, it's (obviously)
> dropped off my radar, but perhaps in the interim we could switch to
> vmf_insert_pfn() and revive the address space series to eventually
> remove the fault handling and vma list altogether.

vmf_insert_pfn() technically isn't supposed to be used for MMIO..

Eg it doesn't do the PAT stuff on x86 that is causing this problem in
the first place.

So doing the address space removing series seems like the best fix. It
has been mislocked for a long time, I suspect there isn't a real
urgent problem beyond we actually have lockdep annoations to catch the
mislocking now.

Jason