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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
