Messages in this thread | | | Date | Fri, 29 May 2015 09:47:24 -0700 | From | Dave Hansen <> | Subject | Re: [PATCH 02/19] x86, fpu: Wrap get_xsave_addr() to make it safer |
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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.
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