lkml.org 
[lkml]   [2014]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCHv4 0/3] Kernel Live Patching
    (2014/11/27 0:27), Josh Poimboeuf wrote:
    > On Wed, Nov 26, 2014 at 10:18:24AM +0100, Jiri Kosina wrote:
    >> On Wed, 26 Nov 2014, Masami Hiramatsu wrote:
    >>
    >>>> Note to Steve:
    >>>> Masami's IPMODIFY patch is heading for -next via your tree. Once it arrives,
    >>>> I'll rebase and make the change to set IPMODIFY. Do not pull this for -next
    >>>> yet. This version (v4) is for review and gathering acks.
    >>>
    >>> BTW, as we discussed IPMODIFY is an exclusive flag. So if we allocate
    >>> ftrace_ops for each function in each patch, it could be conflict each
    >>> other.
    >>
    >> Yup, this corresponds to what Petr brought up yesterday. There are cases
    >> where all solutions (kpatch, kgraft, klp) would allocate multiple
    >> ftrace_ops for a single function entry (think of patching one function
    >> multiple times in a row).
    >>
    >> So it's not as easy as just setting the flag.
    >>
    >>> Maybe we need to have another ops hashtable to find such conflict and
    >>> new handler to handle it.
    >>
    >> If I understand your proposal correctly, that would sound like a hackish
    >> workaround, trying to basically trick the IPMODIFY flag semantics you just
    >> implemented :)
    >
    > I think Masami may be proposing something similar to what we do in
    > kpatch today. We have a single ftrace_ops and handler which is used for
    > all functions. The handler accesses a global hash of kpatch_func
    > structs which is indexed by the original function's IP address.

    Hmm, I think both is OK. kpatch method is less memory consuming and
    will have a bigger overhead. However, as Steven talked at Plumbers Conf.,
    he will introduce a direct code modifying interface for ftrace. After
    that is introduced, we don't need to care about performance degradation
    by patching :)

    > It actually works out pretty well because it nicely encapsulates the
    > knowledge about which functions are patched in a single place. And it
    > makes it easy to track function versions (for incremental patching and
    > rollback).
    >
    >> What I'd propose instead is to make sure that we always have
    >> just a ftrace_ops per function entry, and only update the pointers there
    >> as necessary. Fortunately we can do the switch atomically, by making use
    >> of ->private.
    >
    > But how would you update multiple functions atomically, to enforce
    > per-thread consistency?

    At this point, both can do it atomically. We just need an atomic flag
    for applying patches.

    Thank you,


    --
    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Research Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com




    \
     
     \ /
      Last update: 2014-11-27 11:41    [W:5.374 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site