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SubjectRe: [PATCH v3 00/20] Speculative page faults
On Wed, Oct 04, 2017 at 08:50:49AM +0200, Laurent Dufour wrote:
> On 25/09/2017 18:27, Alexei Starovoitov wrote:
> > On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> > <ldufour@linux.vnet.ibm.com> wrote:
> >> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
> >> feedback on this series.
> >>
> >> Is there a chance to get it moved upstream ?
> >
> > what is the status ?
> > We're eagerly looking forward for this set to land,
> > since we have several use cases for tracing that
> > will build on top of this set as discussed at Plumbers.
>
> Hi Alexei,
>
> Based on Plumber's note [1], it sounds that the use case is tied to the BPF
> tracing where a call tp find_vma() call will be made on a process's context
> to fetch user space's symbols.
>
> Am I right ?
> Is the find_vma() call made in the context of the process owning the mm
> struct ?

Hi Laurent,

we're thinking about several use cases on top of your work.
First one is translation of user address to file_handle where
we need to do find_vma() from preempt_disabled context of bpf program.
My understanding that srcu should solve that nicely.
Second is making probe_read() to try harder when address is causing
minor fault. We're thinking that find_vma() followed by some new
light weight filemap_access() that doesn't sleep will do the trick.
In both cases the program will be accessing current->mm

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