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Re: [Qemu-devel] [PATCH 00/23] userfaultfd v4

From: Richard Weinberger
Subject: Re: [Qemu-devel] [PATCH 00/23] userfaultfd v4
Date: Tue, 19 May 2015 23:59:42 +0200

On Tue, May 19, 2015 at 11:38 PM, Andrew Morton
<address@hidden> wrote:
> On Thu, 14 May 2015 19:30:57 +0200 Andrea Arcangeli <address@hidden> wrote:
>> This is the latest userfaultfd patchset against mm-v4.1-rc3
>> 2015-05-14-10:04.
> It would be useful to have some userfaultfd testcases in
> tools/testing/selftests/.  Partly as an aid to arch maintainers when
> enabling this.  And also as a standalone thing to give people a
> practical way of exercising this interface.
> What are your thoughts on enabling userfaultfd for other architectures,
> btw?  Are there good use cases, are people working on it, etc?

UML is using SIGSEGV for page faults.
i.e. the UML processes receives a SIGSEGV, learns the faulting address
from the mcontext
and resolves the fault by installing a new mapping.

If userfaultfd is faster that the SIGSEGV notification it could speed
up UML a bit.
For UML I'm only interested in the notification, not the resolving
part. The "missing"
data is present, only a new mapping is needed. No copy of data.

Andrea, what do you think?


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