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Date: Wed, 27 Sep 2017 10:40:21 -0400 From: Boris Ostrovsky <boris.ostrovsky@...cle.com> To: Joao Martins <joao.m.martins@...cle.com>, linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, Juergen Gross <jgross@...e.com>, Andy Lutomirski <luto@...capital.net> Subject: Re: [PATCH v4 2/3] x86/xen/time: setup vcpu 0 time info page > +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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