Messages in this thread | | | Subject | Re: [PATCH v7 04/27] x86/fpu/xstate: Introduce XSAVES system states | From | Dave Hansen <> | Date | Thu, 6 Jun 2019 15:08:23 -0700 |
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On 6/6/19 3:04 PM, Andy Lutomirski wrote: >> But, that seems broken. If we have supervisor state, we can't >> always defer the load until return to userspace, so we'll never?? >> have TIF_NEED_FPU_LOAD. That would certainly be true for >> cet_kernel_state. > > Ugh. I was sort of imagining that we would treat supervisor state completely separately from user state. But can you maybe give examples of exactly what you mean? > >> It seems like we actually need three classes of XSAVE states: 1. >> User state > > This is FPU, XMM, etc, right?
Yep.
>> 2. Supervisor state that affects user mode > > User CET?
Yep.
>> 3. Supervisor state that affects kernel mode > > Like supervisor CET? If we start doing supervisor shadow stack, the > context switches will be real fun. We may need to handle this in > asm.
Yeah, that's what I was thinking.
I have the feeling Yu-cheng's patches don't comprehend this since Sebastian's patches went in after he started working on shadow stacks.
> Where does PKRU fit in? Maybe we can treat it as #3?
I thought Sebastian added specific PKRU handling to make it always eager. It's actually user state that affect kernel mode. :)
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