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

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Date:   Sat, 15 Oct 2022 11:46:49 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES
 supervisor states

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.

> +	"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. :)

> +	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.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette