[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Bug#762195: libc6: libpthread: hardware-assisted lock elision hazardous on x86



On Fri, 19 Sep 2014, Aurelien Jarno wrote:
> It looks like Intel did crap there, and that the GNU libc has to handle
> this crap. The microcode update could have stop advertising the
> instructions while still supporting them...

They had their reasons to not do it that way, I suppose.  I don't think the
Intel microcode teams optimize for any other update mode than "do it at
firmware init or kernel init".

What gets me angry is that, as usual, we had no idea of what the microcode
update would do, since we also had no idea of what errata it was supposed to
fix.

> > Therefore, due to erratum HSD136 and the lack of widespread use of microcode
> > updates, libpthread-2.19 must stop using HLE on the problematic Intel
> > processors.
> 
> I will try to work on a patch but this won't be enough, until the users
> reboot their system it's very likely that some process using the old
> libpthread with HLE enabled will remain.

I can live with that, and I think I can prepare a patch if you want me to.
What I cannot do is test it.

BTW, I believe it should be possible to warn the user in postinst.  We just
need to look for the hle flag in /proc/cpuinfo when upgrading from a package
version that did not have the blacklist in place.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh


Reply to: