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Re: [PATCH linux 1/2] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32
- To: Dongli Zhang <dongli.zhang@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Tue, 12 Oct 2021 13:17:41 -0400
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- Delivery-date: Tue, 12 Oct 2021 17:19:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/12/21 3:24 AM, Dongli Zhang wrote:
The sched_clock() can be used very early since upstream
commit 857baa87b642 ("sched/clock: Enable sched clock early"). In addition,
with upstream commit 38669ba205d1 ("x86/xen/time: Output xen sched_clock
time from 0"), kdump kernel in Xen HVM guest may panic at very early stage
when accessing &__this_cpu_read(xen_vcpu)->time as in below:
Please drop "upstream". It's always upstream here.
+
+ /*
+ * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'
+ * and the VM would use them until xen_vcpu_setup() is used to
+ * allocate/relocate them at arbitrary address.
+ *
+ * However, when Xen HVM guest panic on vcpu >= MAX_VIRT_CPUS,
+ * per_cpu(xen_vcpu, cpu) is still NULL at this stage. To access
+ * per_cpu(xen_vcpu, cpu) via xen_clocksource_read() would panic.
+ *
+ * Therefore we delay xen_hvm_init_time_ops() to
+ * xen_hvm_smp_prepare_boot_cpu() when boot vcpu is >= MAX_VIRT_CPUS.
+ */
+ if (xen_vcpu_nr(0) >= MAX_VIRT_CPUS)
What about always deferring this when panicing? Would that work?
Deciding whether to defer based on cpu number feels a bit awkward.
-boris
+ pr_info("Delay xen_hvm_init_time_ops() as kernel is running on
vcpu=%d\n",
+ xen_vcpu_nr(0));
+ else
+ xen_hvm_init_time_ops();
+
xen_hvm_init_mmu_ops();
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