Re: [PATCH v10 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states

Yu-cheng Yu
2020-07-23T16:22:17Z

On Thu, 2020-07-23 at 09:10 -0700, Sean Christopherson wrote:
> On Wed, Apr 29, 2020 at 03:07:09PM -0700, Yu-cheng Yu wrote:
> > diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> > index 12c9684d59ba..47f603729543 100644
> > --- a/arch/x86/include/asm/msr-index.h
> > +++ b/arch/x86/include/asm/msr-index.h
> > @@ -885,4 +885,22 @@
> > #define MSR_VM_IGNNE 0xc0010115
> > #define MSR_VM_HSAVE_PA 0xc0010117
> >
> > +/* Control-flow Enforcement Technology MSRs */
> > +#define MSR_IA32_U_CET 0x6a0 /* user mode cet setting */
> > +#define MSR_IA32_S_CET 0x6a2 /* kernel mode cet setting */
> > +#define MSR_IA32_PL0_SSP 0x6a4 /* kernel shstk pointer */
> > +#define MSR_IA32_PL1_SSP 0x6a5 /* ring-1 shstk pointer */
> > +#define MSR_IA32_PL2_SSP 0x6a6 /* ring-2 shstk pointer */
> > +#define MSR_IA32_PL3_SSP 0x6a7 /* user shstk pointer */
> > +#define MSR_IA32_INT_SSP_TAB 0x6a8 /* exception shstk table */
> > +
> > +/* MSR_IA32_U_CET and MSR_IA32_S_CET bits */
> > +#define MSR_IA32_CET_SHSTK_EN 0x0000000000000001ULL
>
> Can we drop the MSR_IA32 prefix for the individual bits? Mostly to yield
> shorter line lengths, but also because it's more or less redundant info,
> and in some ways unhelpful as it's hard to quickly differentiate between
> "this is an MSR index" and "this is a bit/mask for an MSR".

Agree!

>
> My vote would also be to use BIT() or BIT_ULL(). The SDM defines the flags
> by their (decimal) bit number. Manually converting the bits to masks makes
> it difficult to check for correctness.
>
> E.g.
>
> #define CET_SHSTK_EN BIT(0)
> #define CET_WRSS_EN BIT(1)
> #define CET_ENDBR_EN BIT(2)
> #define CET_LEG_IW_EN BIT(3)
> #define CET_NO_TRACK_EN BIT(4)
> #define CET_WAIT_ENDBR BIT(5)

I will change them.

>
> > +#define MSR_IA32_CET_WRSS_EN 0x0000000000000002ULL
> > +#define MSR_IA32_CET_ENDBR_EN 0x0000000000000004ULL
> > +#define MSR_IA32_CET_LEG_IW_EN 0x0000000000000008ULL
> > +#define MSR_IA32_CET_NO_TRACK_EN 0x0000000000000010ULL
> > +#define MSR_IA32_CET_WAIT_ENDBR 0x00000000000000800UL
> > +#define MSR_IA32_CET_BITMAP_MASK 0xfffffffffffff000ULL
>
> This particular define, the so called BITMAP_MASK, is no longer used in the
> IBT series. IMO it'd be better off dropping this mask as it's not clear
> from the name that this is really nothing more than a mask for a virtual
> address, e.g. at first glance (for someone without CET knowledge) it looks
> like bits 63:12 hold a bitmap as opposed to holding a pointer to a bitmap.

I will remove this.

Thanks,
Yu-cheng