On 13.01.2022 14:17, Jan Beulich wrote:
> Except in the "clocksource=tsc" case we can replace the indirect calls
> involved in accessing the platform timers by direct ones, as they get
> established once and never changed. To also cover the "tsc" case, invoke
> what read_tsc() resolves to directly. In turn read_tsc() then becomes
> unreachable and hence can move to .init.*.
>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
As this actually amends the IBT work, I would have hoped for it to be
viewed as useful. Of course if accepted in general, it would now want
to have __initconst_cf_clobber annotation addition included. Albeit
there's a slight complication: Some of the structures are written to,
so those couldn't really be "const".
Jan
> ---
> v2: Avoid altcall patching becoming conditional.
>
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -66,6 +66,7 @@ struct platform_timesource {
> char *id;
> char *name;
> u64 frequency;
> + /* This hook may only be invoked via the read_counter() wrapper! */
> u64 (*read_counter)(void);
> s64 (*init)(struct platform_timesource *);
> void (*resume)(struct platform_timesource *);
> @@ -578,7 +579,7 @@ static s64 __init init_tsc(struct platfo
> return ret;
> }
>
> -static u64 read_tsc(void)
> +static uint64_t __init read_tsc(void)
> {
> return rdtsc_ordered();
> }
> @@ -810,6 +811,18 @@ static s_time_t __read_platform_stime(u6
> return (stime_platform_stamp + scale_delta(diff, &plt_scale));
> }
>
> +static uint64_t read_counter(void)
> +{
> + /*
> + * plt_tsc is put in use only after alternatives patching has occurred,
> + * hence we can't invoke read_tsc() that way. Special case it here, open-
> + * coding the function call at the same time.
> + */
> + return plt_src.read_counter != read_tsc
> + ? alternative_call(plt_src.read_counter)
> + : rdtsc_ordered();
> +}
> +
> static void plt_overflow(void *unused)
> {
> int i;
> @@ -818,7 +831,7 @@ static void plt_overflow(void *unused)
>
> spin_lock_irq(&platform_timer_lock);
>
> - count = plt_src.read_counter();
> + count = read_counter();
> plt_stamp64 += (count - plt_stamp) & plt_mask;
> plt_stamp = count;
>
> @@ -854,7 +867,7 @@ static s_time_t read_platform_stime(u64
> ASSERT(!local_irq_is_enabled());
>
> spin_lock(&platform_timer_lock);
> - plt_counter = plt_src.read_counter();
> + plt_counter = read_counter();
> count = plt_stamp64 + ((plt_counter - plt_stamp) & plt_mask);
> stime = __read_platform_stime(count);
> spin_unlock(&platform_timer_lock);
> @@ -872,7 +885,7 @@ static void platform_time_calibration(vo
> unsigned long flags;
>
> spin_lock_irqsave(&platform_timer_lock, flags);
> - count = plt_stamp64 + ((plt_src.read_counter() - plt_stamp) & plt_mask);
> + count = plt_stamp64 + ((read_counter() - plt_stamp) & plt_mask);
> stamp = __read_platform_stime(count);
> stime_platform_stamp = stamp;
> platform_timer_stamp = count;
> @@ -883,10 +896,10 @@ static void resume_platform_timer(void)
> {
> /* Timer source can be reset when backing from S3 to S0 */
> if ( plt_src.resume )
> - plt_src.resume(&plt_src);
> + alternative_vcall(plt_src.resume, &plt_src);
>
> plt_stamp64 = platform_timer_stamp;
> - plt_stamp = plt_src.read_counter();
> + plt_stamp = read_counter();
> }
>
> static void __init reset_platform_timer(void)
>
>
