Re: [PATCH v2 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states

Edgecombe, Rick P
2022-10-17T18:57:32Z

On Sat, 2022-10-15 at 11:46 +0200, Borislav Petkov wrote:
> On Thu, Sep 29, 2022 at 03:29:02PM -0700, Rick Edgecombe wrote:
> > Both XSAVE state components are supervisor states, even the state
> > controlling user-mode operation. This is a departure from earlier
> > features
> > like protection keys where the PKRU state a normal user (non-
> > supervisor)
>
> ^^^^^
>
> A verb is missing in that sentence.

Oops yes.

>
> > + "x87 floating point registers" ,
> > + "SSE registers" ,
> > + "AVX registers" ,
> > + "MPX bounds registers" ,
> > + "MPX CSR" ,
> > + "AVX-512 opmask" ,
> > + "AVX-512 Hi256" ,
> > + "AVX-512 ZMM_Hi256" ,
> > + "Processor Trace (unused)" ,
> > + "Protection Keys User registers" ,
> > + "PASID state" ,
> > + "Control-flow User registers" ,
> > + "Control-flow Kernel registers (unused)" ,
> > + "unknown xstate feature" ,
> > + "unknown xstate feature" ,
> > + "unknown xstate feature" ,
> > + "unknown xstate feature" ,
> > + "AMX Tile config" ,
> > + "AMX Tile data" ,
> > + "unknown xstate feature" ,
>
> What Kees said. :)

Sure, I'll adjust the comma.

>
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_YMM, struct
> > ymmh_struct);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_BNDREGS, struct
> > mpx_bndreg_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_BNDCSR, struct
> > mpx_bndcsr_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_OPMASK, struct
> > avx_512_opmask_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_ZMM_Hi256, struct
> > avx_512_zmm_uppers_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_Hi16_ZMM, struct
> > avx_512_hi16_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_PKRU, struct
> > pkru_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_PASID, struct
> > ia32_pasid_state);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_XTILE_CFG, struct
> > xtile_cfg);
> > + XCHECK_SZ(&chked, sz, nr, XFEATURE_CET_USER, struct
> > cet_user_state);
>
> That looks silly. I wonder if you could do:
>
> switch (nr) {
> case XFEATURE_YMM: XCHECK_SZ(sz, XFEATURE_YMM, struct
> ymmh_struct); return;
> case XFEATURE_BNDREGS: XCHECK_SZ(sz, XFEATURE_BNDREGS,
> struct mpx_bndreg_state); return;
> case ...
> ...
> default:
> /* that falls into the WARN etc */
>
> and then you get rid of the if check in the macro itself and leave
> the
> macro be a dumb, unconditional one.
>
> Hmmm.
>

Hmm yea. Another reason the actual define is passed in is that the
macro want's to stringify the XFEATURE define in order to generate the
message like this:
XFEATURE_YMM: struct is 123 bytes, cpu state is 456 bytes

The exact format of the message is probably not too critical though. If
instead it used xfeature_names[], it could be:
[AVX registers]: struct is 123 bytes, cpu state is 456 bytes

The full block looks like (like you had):
switch (nr) {
case XFEATURE_YMM: return XCHECK_SZ(sz, nr, struct ymmh_struct);
case XFEATURE_BNDREGS: return XCHECK_SZ(sz, nr, struct
mpx_bndreg_state);
case XFEATURE_BNDCSR: return XCHECK_SZ(sz, nr, struct
mpx_bndcsr_state);
case XFEATURE_OPMASK: return XCHECK_SZ(sz, nr, struct
avx_512_opmask_state);
case XFEATURE_ZMM_Hi256: return XCHECK_SZ(sz, nr, struct
avx_512_zmm_uppers_state);
case XFEATURE_Hi16_ZMM: return XCHECK_SZ(sz, nr, struct
avx_512_hi16_state);
case XFEATURE_PKRU: return XCHECK_SZ(sz, nr, struct pkru_state);
case XFEATURE_PASID: return XCHECK_SZ(sz, nr, struct
ia32_pasid_state);
case XFEATURE_XTILE_CFG: return XCHECK_SZ(sz, nr, struct xtile_cfg);
case XFEATURE_CET_USER: return XCHECK_SZ(sz, nr, struct
cet_user_state);
case XFEATURE_XTILE_DATA: check_xtile_data_against_struct(sz); return
true;
default:
WARN_ONCE(1, "no structure for xstate: %d\n", nr);
XSTATE_WARN_ON(1);
return false;
}

I like how it fits the XFEATURE_XTILE_DATA check in with the rest.

Thanks!