Messages in this thread | | | Date | Fri, 30 Jan 2015 14:43:09 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 0/3]: x86, fpu: unlazy_fpu fixes/cleanups |
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On 01/30, Oleg Nesterov wrote: > > On 01/30, Oleg Nesterov wrote: > > > > On 01/29, Dave Hansen wrote: > > > > > > On 01/29/2015 01:56 PM, Oleg Nesterov wrote: > > > > --- x/arch/x86/kernel/traps.c > > > > +++ x/arch/x86/kernel/traps.c > > > > @@ -313,7 +313,7 @@ dotraplinkage void do_bounds(struct pt_r > > > > * It is not directly accessible, though, so we need to > > > > * do an xsave and then pull it out of the xsave buffer. > > > > */ > > > > - fpu_save_init(&tsk->thread.fpu); > > > > + unlazy_fpu(tsk); > > > > xsave_buf = &(tsk->thread.fpu.state->xsave); > > > ... > > > > bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR); > > > > > > Hmm, if the the thread was not using the FPU, and this fails to save > > > anything in to the xsave_buf, what will bndcsr point to? It _looks_ to > > > me like it will just point to uninitialized data since the xsave never > > > happened. > > > > > > Fenghua, shouldn't get_xsave_addr() be checking the xstate bit against > > > the xsave->xstate_bv? > > > > Can't really comment, but let me clarify what I meant just in case... > > > > If it was not using FPU then I guess do_bounds() can't happen. However, > > it can be preempted after conditional_sti(). fpu_save_init() is obviously > > wrong unless __thread_has_fpu() == T, and this can be false if !eagerfpu > > or if we add TIF_LOAD_FPU (defer FPU restore until return to userspace). > > Forgot to mention... and if we use unlazy_fpu() we should not worry about > preemption/__thread_has_fpu, we can rely on __save_init_fpu() in __switch_to() > and/or __thread_has_fpu() check in unlazy_fpu(). > > But I am afraid I misunderstood your concerns, sorry for noise in this case.
Yes ;)
Perhaps do_bounds() needs the additional
if (!used_math()) goto exit_trap;
check?
Oleg.
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