Re: [patch V4 part 1 27/36] arm64: Prepare arch_nmi_enter() for recursion

Mathieu Desnoyers
2020-05-13T23:28:38Z

----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@linutronix.de wrote:

> +#define arch_nmi_enter() \
[...] \
> + ___hcr = read_sysreg(hcr_el2); \
> + if (!(___hcr & HCR_TGE)) { \
> + write_sysreg(___hcr | HCR_TGE, hcr_el2); \
> + isb(); \

Why is there an isb() above ^ ....

> + } \
> + /* \
[...]
> -#define arch_nmi_exit() \
[...]
> + /* \
> + * Make sure ___ctx->cnt release is visible before we \
> + * restore the sysreg. Otherwise a new NMI occurring \
> + * right after write_sysreg() can be fooled and think \
> + * we secured things for it. \
> + */ \
> + barrier(); \
> + if (!___ctx->cnt && !(___hcr & HCR_TGE)) \
> + write_sysreg(___hcr, hcr_el2); \

And not here ?

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.