Re: [RFCv2 04/10] x86/mm: Introduce X86_THREAD_LAM_U48 and X86_THREAD_LAM_U57

Peter Zijlstra
2022-05-11T07:04:08Z

On Wed, May 11, 2022 at 05:27:45AM +0300, Kirill A. Shutemov wrote:

> +#define LAM_NONE 0
> +#define LAM_U57 1
> +#define LAM_U48 2

> +#define X86_THREAD_LAM_U48 0x1
> +#define X86_THREAD_LAM_U57 0x2

Seriously pick an order and stick with it. I would suggest keeping the
hardware order and then you can do:

> +static inline unsigned long lam_to_cr3(u8 lam)
> +{
> + switch (lam) {
> + case LAM_NONE:
> + return 0;
> + case LAM_U57:
> + return X86_CR3_LAM_U57;
> + case LAM_U48:
> + return X86_CR3_LAM_U48;
> + default:
> + WARN_ON_ONCE(1);
> + return 0;
> + }

return (lam & 0x3) << X86_CR3_LAM_U57;

> +}
> +
> +static inline u8 cr3_to_lam(unsigned long cr3)
> +{
> + if (cr3 & X86_CR3_LAM_U57)
> + return LAM_U57;
> + if (cr3 & X86_CR3_LAM_U48)
> + return LAM_U48;
> + return 0;

return (cr3 >> X86_CR3_LAM_U57) & 0x3;

> +}

and call it a day, or something.

I'm still not liking LAM(e), I'm thikning it's going to create more
problems than it solves.