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

Frederic Weisbecker
2020-05-15T14:04:44Z

On Wed, May 13, 2020 at 07:28:34PM -0400, Mathieu Desnoyers wrote:
> ----- 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 ?

I have to defer to Will on this detail...