Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 5 Mar 2015 16:14:42 +0100 | From | Oleg Nesterov <> | Subject | Re: Oops with tip/x86/fpu |
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On 03/04, Borislav Petkov wrote: > > On Wed, Mar 04, 2015 at 08:06:51PM +0100, Oleg Nesterov wrote: > > Thanks. I'll try to investigate tomorrow. > > > > Well, the kernel crashes because xrstor_state() is buggy, Quentin already > > has a fix. > > > > But #GP should be explained... > > Could it be one of those conditions for which XRSTORS #GPs, like > > "If XRSTORS attempts to load MXCSR with an illegal value, a > general-protection exception (#GP) occurs." > > for example? I'm looking at the SDM section for XRSTORS. > > I mean, math_state_restore() does init_fpu() and down that road we're > allocating an FPU state ... but we did init_fpu() before too, in > eager_fpu_init(). So what changed?
I _think_ that the difference is that eager_fpu_init()->xrstor_state() was called before apply_alternatives(), so it used XRSTOR.
Note also that (before this commit) restore_fpu_checking() was almost never called right after init_fpu(). If use_eager_fpu() == T.
After this commit the first xrstor_state() uses XRSTORS. And that is how (I think) 'noxsaves' makes the difference.
So. I can be easily wrong, but so far I _think_ that this commit disclosed another problem. And even if I am wrong and this commit is buggy, we need to understand why ;)
I'll try to think about debugging patch, I can't reproduce this problem on my machine...
Oleg.
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