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SubjectRe: [PATCH v4 2/3] x86/xen/time: setup vcpu 0 time info page
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> +static void xen_setup_vsyscall_time_info(void)
> +{
> + struct vcpu_register_time_memory_area t;
> + struct pvclock_vsyscall_time_info *ti;
> + struct pvclock_vcpu_time_info *pvti;
> + int ret;
> +
> + pvti = &__this_cpu_read(xen_vcpu)->time;
> +
> + /*
> + * We check ahead on the primary time info if this
> + * bit is supported hence speeding up Xen clocksource.
> + */
> + if (!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))
> + return;
> +
> + pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

Is it OK to have this flag set if anything below fails?

(I can see in the changelog that apparently at some point I've asked
about this at v1 but I can't remember/find what exactly it was)

-boris

> +
> + ti = (struct pvclock_vsyscall_time_info *)get_zeroed_page(GFP_KERNEL);
> + if (!ti)
> + return;
> +
> + t.addr.v = &ti->pvti;
> +
> + ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, 0, &t);
> + if (ret) {
> + pr_notice("xen: VCLOCK_PVCLOCK not supported (err %d)\n", ret);
> + free_page((unsigned long)ti);
> + return;
> + }
> +
> + /*
> + * If the check above succedded this one should too since it's the
> + * same data on both primary and secondary time infos just different
> + * memory regions. But we still check it in case hypervisor is buggy.
> + */
> + pvti = &ti->pvti;
> + if (!(pvti->flags & PVCLOCK_TSC_STABLE_BIT)) {
> + t.addr.v = NULL;
> + ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
> + 0, &t);
> + if (!ret)
> + free_page((unsigned long)ti);
> +
> + pr_notice("xen: VCLOCK_PVCLOCK not supported (tsc unstable)\n");
> + return;
> + }
> +
> + xen_clock = ti;
> + pvclock_set_pvti_cpu0_va(xen_clock);
> +
> + xen_clocksource.archdata.vclock_mode = VCLOCK_PVCLOCK;
> +}
> +

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