Messages in this thread | | | Date | Fri, 29 May 2015 20:48:29 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 02/19] x86, fpu: Wrap get_xsave_addr() to make it safer |
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* Dave Hansen <dave@sr71.net> wrote:
> On 05/28/2015 01:41 AM, Ingo Molnar wrote: > >> > + union fpregs_state *xstate; > >> > + > >> > + if (!current->thread.fpu.fpstate_active) > >> > + return NULL; > >> > + /* > >> > + * fpu__save() takes the CPU's xstate registers > >> > + * and saves them off to the 'fpu memory buffer. > >> > + */ > >> > + fpu__save(¤t->thread.fpu); > >> > + xstate = ¤t->thread.fpu.state; > >> > + > >> > + return get_xsave_addr(&xstate->xsave, xsave_state); > > Small nit, this would become a lot shorter if you introduced a helper local > > variable: > > > > struct fpu *fpu = ¤t->thread.fpu; > > > > But more importantly, for a generic get_xsave_field_ptr() API, fpu__save() is > > not enough: fpu__save() will only save FPU registers into memory if necessary > > (i.e. if the FPU is already in use), and if you call it on a task with no FPU > > state then it will still have an !fpu->fpstate_active FPU state after the > > call, with random, invalid data in the xsave area. > > But why does this matter? We just did a !fpu.fpstate_active check, so we can't > have a !fpu.fpstate_active before or after the call.
Ah yes, you are right, I missed this:
> >> > + if (!current->thread.fpu.fpstate_active) > >> > + return NULL;
because the usual pattern is:
if (!fpu->fpstate_active) return NULL;
:-)
So your variant is fine too.
Thanks,
Ingo
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