linux-kernel - Re: [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory

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Message-ID: <20200525122607.GC744@ziepe.ca>
Date:   Mon, 25 May 2020 09:26:07 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Peter Xu <peterx@...hat.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, cohuck@...hat.com, cai@....pw
Subject: Re: [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access
 on disabled memory

On Sat, May 23, 2020 at 07:52:57PM -0400, Peter Xu wrote:

> For what I understand now, IMHO we should still need all those handlings of
> FAULT_FLAG_RETRY_NOWAIT like in the initial version.  E.g., IIUC KVM gup will
> try with FOLL_NOWAIT when async is allowed, before the complete slow path.  I'm
> not sure what would be the side effect of that if fault() blocked it.  E.g.,
> the caller could be in an atomic context.

AFAICT FAULT_FLAG_RETRY_NOWAIT only impacts what happens when
VM_FAULT_RETRY is returned, which this doesn't do?

It is not a generic 'do not sleep'

Do you know different?

Jason