Re: linux-next: manual merge of the xen-tip tree with the tip tree

Ingo Molnar
2017-08-31T09:17:03Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -586,6 +586,68 @@ static void xen_write_ldt_entry(struct d
> preempt_enable();
> }
>
> +#ifdef CONFIG_X86_64
> +static struct {
> + void (*orig)(void);
> + void (*xen)(void);
> + bool ist_okay;
> +} trap_array[] = {
> + { debug, xen_xendebug, true },
> + { int3, xen_xenint3, true },
> + { double_fault, xen_double_fault, true },
> +#ifdef CONFIG_X86_MCE
> + { machine_check, xen_machine_check, true },
> +#endif
> + { nmi, xen_nmi, true },
> + { overflow, xen_overflow, false },
> +#ifdef CONFIG_IA32_EMULATION
> + { entry_INT80_compat, xen_entry_INT80_compat, false },
> +#endif
> + { page_fault, xen_page_fault, false },
> + { divide_error, xen_divide_error, false },
> + { bounds, xen_bounds, false },
> + { invalid_op, xen_invalid_op, false },
> + { device_not_available, xen_device_not_available, false },
> + { coprocessor_segment_overrun, xen_coprocessor_segment_overrun, false },
> + { invalid_TSS, xen_invalid_TSS, false },
> + { segment_not_present, xen_segment_not_present, false },
> + { stack_segment, xen_stack_segment, false },
> + { general_protection, xen_general_protection, false },
> + { spurious_interrupt_bug, xen_spurious_interrupt_bug, false },
> + { coprocessor_error, xen_coprocessor_error, false },
> + { alignment_check, xen_alignment_check, false },
> + { simd_coprocessor_error, xen_simd_coprocessor_error, false },
> +#ifdef CONFIG_TRACING
> + { trace_page_fault, xen_trace_page_fault, false },
> +#endif
> +};

Low prio nitpicking, could we please write such table based initializers in a
vertically organized, tabular fashion:

> + { debug, xen_xendebug, true },
> + { int3, xen_xenint3, true },
> + { double_fault, xen_double_fault, true },
> +#ifdef CONFIG_X86_MCE
> + { machine_check, xen_machine_check, true },
> +#endif
> + { nmi, xen_nmi, true },
> + { overflow, xen_overflow, false },
> +#ifdef CONFIG_IA32_EMULATION
> + { entry_INT80_compat, xen_entry_INT80_compat, false },
> +#endif
> + { page_fault, xen_page_fault, false },
> + { divide_error, xen_divide_error, false },
> + { bounds, xen_bounds, false },
> + { invalid_op, xen_invalid_op, false },
> + { device_not_available, xen_device_not_available, false },
> + { coprocessor_segment_overrun, xen_coprocessor_segment_overrun, false },
> + { invalid_TSS, xen_invalid_TSS, false },
> + { segment_not_present, xen_segment_not_present, false },
> + { stack_segment, xen_stack_segment, false },
> + { general_protection, xen_general_protection, false },
> + { spurious_interrupt_bug, xen_spurious_interrupt_bug, false },
> + { coprocessor_error, xen_coprocessor_error, false },
> + { alignment_check, xen_alignment_check, false },
> + { simd_coprocessor_error, xen_simd_coprocessor_error, false },
> +#ifdef CONFIG_TRACING
> + { trace_page_fault, xen_trace_page_fault, false },
> +#endif

... as to me such a table is 100 times more readable - YMMV.

(If checkpatch whinges about col80 then ignore it.)

> +
> +static bool get_trap_addr(unsigned long *addr, unsigned int ist)
> +{
> + unsigned int nr;
> + bool ist_okay = false;
> +
> + /*
> + * Replace trap handler addresses by Xen specific ones.
> + * Check for known traps using IST and whitelist them.
> + * The debugger ones are the only ones we care about.
> + * Xen will handle faults like double_fault, * so we should never see
> + * them. Warn if there's an unexpected IST-using fault handler.
> + */
> + for (nr = 0; nr < ARRAY_SIZE(trap_array); nr++)
> + if (*addr == (unsigned long)trap_array[nr].orig) {
> + *addr = (unsigned long)trap_array[nr].xen;
> + ist_okay = trap_array[nr].ist_okay;
> + break;
> + }

And here I think we could do a more readable variant:

static bool get_trap_addr(void **addr, unsigned int ist)
...
struct trap_array_entry *entry = trap_array + nr;

if (*addr == entry->orig) {
*addr = entry->xen;
ist_okay = entry->ist_okay;
break;
}

I believe 'void **' is the natural type that avoids the type casts, and the
'trap_array_entry' name has to be defined in the array definition further above.

Totally untested though.

Thanks,

Ingo