Re: [PATCH v3 06/19] x86/startup_64: Drop global variables keeping track of LA57 state

Ard Biesheuvel
2024-02-11T22:37:05Z

On Sat, 10 Feb 2024 at 11:41, Borislav Petkov <bp@alien8.de> wrote:
>
> On Fri, Feb 09, 2024 at 01:55:02PM +0000, Ard Biesheuvel wrote:
> > I was trying to get rid of global variable assignments and accesses
> > from the 1:1 mapping, but since we cannot get rid of those entirely,
> > we might just keep __pgtable_l5_enabled but use RIP_REL_REF() in the
> > accessors, and move the assignment to the asm startup code.
>
> Yeah.
>
> > asm(ALTERNATIVE_TERNARY(
> > "movq %%cr4, %[reg] \n\t btl %[la57], %k[reg]" CC_SET(c),
> > %P[feat], "stc", "clc")
> > : [reg] "=r" (r), CC_OUT(c) (ret)
> > : [feat] "i" (X86_FEATURE_LA57),
> > [la57] "i" (X86_CR4_LA57_BIT)
> > : "cc");
>
> Creative :)
>
> > but we'd still have two versions in that case.
>
> Yap. RIP_REL_REF() ain't too bad ...
>

We can actually rip all of that stuff out, and have only a single
implementation of pgtable_l5_enabled() that is not based on a variable
at all. It results in a nice cleanup, but I'll keep it as a separate
patch in the next revision so we can easily drop it if preferred.