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

[Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>]

On 20 January 2015 at 10:52, Ian Campbell <ian.campbell@xxxxxxxxxx> 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>
> Cc: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> RFC since I'm not sure how extreme our reaction ought to be here, e.g.
> I considered domain_crash() or even panic() when in a debug build. A
> XENLOG_DEBUG message is about the most benign of the options.
>
> Jan/Keir, although this is ARM specific I'd welcome your views as
> x86/REST maintainers.
>
> Ard, I've not actually run this -- any chance you could re-b0rk your
> Tianocore image and give it a go?

I get a bunch of lines in my log looking like

(XEN) traps.c:1162:d4v0 d4v0: deprecated hypercall 16

so

Tested-by: Ard Biesheuvel <ard@xxxxxxxxxx>

-- 
Ard.

> ---
>  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 ad046e8..89cbde6 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1148,6 +1148,22 @@ 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 %ld\n",
> +             current, (unsigned long)op);
> +    return -ENOSYS;
> +}
> +
>  typedef register_t (*arm_hypercall_fn_t)(
>      register_t, register_t, register_t, register_t, register_t);
>
> @@ -1167,15 +1183,29 @@ 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)                   \
> +    [ __HYPERVISOR_##_name ] = {                                \
> +        .fn = (arm_hypercall_fn_t) &do_deprecated_hypercall,    \
> +        .nr_args = _nr_args,                                    \
> +    }
> +
>  static arm_hypercall_t arm_hypercall_table[] = {
>      HYPERCALL(memory_op, 2),
>      HYPERCALL(domctl, 1),
>      HYPERCALL(sched_op, 2),
> +    HYPERCALL_DEPRECATED(sched_op_compat, 2),
>      HYPERCALL(console_io, 3),
>      HYPERCALL(xen_version, 2),
>      HYPERCALL(xsm_op, 1),
>      HYPERCALL(event_channel_op, 2),
> +    HYPERCALL_DEPRECATED(event_channel_op_compat, 1),
>      HYPERCALL(physdev_op, 2),
> +    HYPERCALL_DEPRECATED(physdev_op_compat, 1),
>      HYPERCALL(sysctl, 2),
>      HYPERCALL(hvm_op, 2),
>      HYPERCALL(grant_table_op, 3),
> --
> 1.7.10.4
>

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