Re: [Xen-devel] [PATCH v2] xen: arm: Log a warning message when a deprecated hypercall is used

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 26/06/2015 13:39, Ian Campbell wrote:
> A few folks have been caught out by OSes which call e.g.
> HYPERVISOR_event_channel_op_compat which has been deprecated since
> 3.2.2 (i.e. long before Xen on ARM). Existing x86 code can still
> safely and quietly using those calls, waiting for an unsuspecting ARM
> porter to turn up and trip over it. This turns out to be rather
> perplexing when it happens, since it can be obscured e.g. by various
> conditionals like __XEN_INTERFACE_VERSION__ what is actually being
> called.
>
> Note that I'm making a distinction here between hypercalls which are
> simply not used/implemented on arm (yet) and those which were
> deprecated and replaced by a newer variant prior to Xen on ARM even
> being invented.  The latter will never be implemented on ARM and have
> non-deprecated aliases leading to confusion so those are the ones for
> which a warning is useful.
>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Tested-by: Ard Biesheuvel <ard@xxxxxxxxxx>
> Cc: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> v2:
>     - Use correct format code (I didn't yet shave the yakk of providing
>       PRIxREG et al).
>     - Settle on just a debug message for now.
>
> Ard tested the last version, but this one is unchanged enough that
> I've retained it.
> ---
>   xen/arch/arm/traps.c |   30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 258d4c5..06fb40f 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1171,6 +1171,22 @@ die:
>   }
>   #endif
>
> +static register_t do_deprecated_hypercall(void)
> +{
> +    struct cpu_user_regs *regs = guest_cpu_user_regs();
> +    const register_t op =
> +#ifdef CONFIG_ARM_64
> +        !is_32bit_domain(current->domain) ?
> +            regs->x16
> +        :
> +#endif
> +            regs->r12;
> +
> +    gdprintk(XENLOG_DEBUG, "%pv: deprecated hypercall %lu\n",
> +             current, (unsigned long)op);
> +    return -ENOSYS;
> +}
> +
>   typedef register_t (*arm_hypercall_fn_t)(
>       register_t, register_t, register_t, register_t, register_t);
>
> @@ -1190,15 +1206,29 @@ typedef struct {
>           .fn = (arm_hypercall_fn_t) &do_arm_ ## _name,                \
>           .nr_args = _nr_args,                                         \
>       }
> +/*
> + * Only use this for hypercalls which were deprecated (i.e. replaced
> + * by something else) before Xen on ARM was created, i.e. *not* for
> + * hypercalls which are simply not yet used on ARM.
> + */
> +#define HYPERCALL_DEPRECATED(_name, _nr_args)                   \
I guess the parameter __nr_args is just here for completeness? If so:

Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>

Regards,

--
Julien Grall

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