From: Peter Xu <peterx@redhat.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Alex Williamson <alex.williamson@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
cohuck@redhat.com, cai@lca.pw,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory
Date: Mon, 25 May 2020 11:11:42 -0400 [thread overview]
Message-ID: <20200525151142.GE1058657@xz-x1> (raw)
In-Reply-To: <20200525144651.GE744@ziepe.ca>
On Mon, May 25, 2020 at 11:46:51AM -0300, Jason Gunthorpe wrote:
> On Mon, May 25, 2020 at 10:28:06AM -0400, Peter Xu wrote:
> > On Mon, May 25, 2020 at 09:26:07AM -0300, Jason Gunthorpe wrote:
> > > 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?
> >
> > Yes, that's why I think we should still properly return VM_FAULT_RETRY if
> > needed.. because IMHO it is still possible that the caller calls with
> > FAULT_FLAG_RETRY_NOWAIT.
> >
> > My understanding is that FAULT_FLAG_RETRY_NOWAIT majorly means:
> >
> > - We cannot release the mmap_sem, and,
> > - We cannot sleep
>
> Sleeping looks fine, look at any FS implementation of fault, say,
> xfs. The first thing it does is xfs_ilock() which does down_write().
Yeah. My wild guess is that maybe fs code will always be without
FAULT_FLAG_RETRY_NOWAIT so it's safe to sleep unconditionally (e.g., I think
the general #PF should be fine to sleep in fault(); gup should be special, but
I didn't observe any gup code called upon file systems)?
Or I must have missed something important...
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2020-05-25 15:11 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 19:17 [PATCH v3 0/3] vfio-pci: Block user access to disabled device MMIO Alex Williamson
2020-05-22 19:17 ` [PATCH v3 1/3] vfio/type1: Support faulting PFNMAP vmas Alex Williamson
2020-05-22 19:17 ` [PATCH v3 2/3] vfio-pci: Fault mmaps to enable vma tracking Alex Williamson
2020-05-22 19:17 ` [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory Alex Williamson
2020-05-23 19:34 ` Peter Xu
2020-05-23 23:06 ` Alex Williamson
2020-05-23 23:52 ` Peter Xu
2020-05-24 0:02 ` Peter Xu
2020-05-25 12:26 ` Jason Gunthorpe
2020-05-25 14:28 ` Peter Xu
2020-05-25 14:46 ` Jason Gunthorpe
2020-05-25 15:11 ` Peter Xu [this message]
2020-05-25 16:56 ` Jason Gunthorpe
2020-05-25 20:56 ` John Hubbard
2020-05-26 0:37 ` Jason Gunthorpe
2020-05-26 0:46 ` John Hubbard
2020-05-26 13:49 ` Peter Xu
2020-05-26 14:32 ` Alex Williamson
2020-05-26 14:46 ` Peter Xu
2020-05-26 15:53 ` Jason Gunthorpe
2020-05-26 15:57 ` Alex Williamson
2020-05-22 22:08 ` [PATCH v3 0/3] vfio-pci: Block user access to disabled device MMIO Qian Cai
2020-05-22 22:25 ` Alex Williamson
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