Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

[Mikael Pettersson]

Chris Wright writes:
 > * H. Peter Anvin (hpa@xxxxxxxxx) wrote:
 > > Suresh Siddha wrote:
 > >>
 > >> hpa, What is the virtualization problem? Are you referring to perf problem?
 > >> As you noted, regular non-rt signal handlers won't need this cpuid check. It's
 > >> needed only for those who manually look at non-rt signal frames and interpret it.
 > >> And also, they can do this check only once and not everytime.
 > >>
 > >
 > > No, relying on CPUID and vdso both have implications for virtualization.
 > 
 > hmm, what implications?  cpuid is dealt with already.

By whom?

Case in point: only a few weeks ago, we (as in LKML hackers) tried
to debug a user's bug report. Something very strange seemed to be
going on. It turned out the user was actually using a virtualisation
engine (qemu, not the latest) which presented highly inconsistent
cpuid data to the kernel, causing major confusion.

So I agree with hpa. The kernel has decided to use a particular
sigframe layout. It should communicate this to user-space in a robust
manner that is independent of how the kernel arrived at this decision.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/