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Date: Fri, 01 May 2015 14:55:17 -0400
From: Boris Ostrovsky <boris.ostrovsky@...cle.com>
To: "Ouyang Zhaowei (Charles)" <ouyangzhaowei@...wei.com>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
David Vrabel <david.vrabel@...rix.com>
CC: linux-kernel@...r.kernel.org,
Dingweiping <weiping.ding@...wei.com>,
Yanqiangjun <yanqiangjun@...wei.com>, jinjian@...wei.com,
herongguang.he@...wei.com
Subject: Re: [PATCH] xen: vcpu_info reinit error after 'xl save -c' & 'xl
restore' on PVOPS VM which has multi-cpu
On 04/30/2015 03:27 AM, Ouyang Zhaowei (Charles) wrote:
>
> On 2015.4.29 5:31, Boris Ostrovsky wrote:
>> On 04/28/2015 08:30 AM, Ouyang Zhaowei (Charles) wrote:
>>> On 2015.4.26 7:31, Boris Ostrovsky wrote:
>>>> On 04/24/2015 05:30 AM, Ouyang Zhaowei (Charles) wrote:
>>>>> If a PVOPS VM has multi-cpu the vcpu_info of cpu0 is the member of the structure HYPERVISOR_shared_info,
>>>>> and the others is not, but after 'xl save -c/restore' the vcpu_info will be reinitialized,
>>>>> the vcpu_info of all the vcpus will be considered as the member of HYPERVISOR_shared_info.
>>>>> This will cause the cpu1 and other cpu keep receiving interrupts, and the cpu0 is waiting them to
>>>>> finish the job.
>>>>> So we do not reinit the vcpu_info when PVOPS vm is doing 'xl save -c/restore'.
>>>>>
>>>>> Signed-off-by: Charles Ouyang <ouyangzhaowei@...wei.com>
>>>>> ---
>>>>> arch/x86/xen/suspend.c | 3 ++-
>>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
>>>>> index d949769..b2bed45 100644
>>>>> --- a/arch/x86/xen/suspend.c
>>>>> +++ b/arch/x86/xen/suspend.c
>>>>> @@ -32,7 +32,8 @@ static void xen_hvm_post_suspend(int suspend_cancelled)
>>>>> {
>>>>> #ifdef CONFIG_XEN_PVHVM
>>>>> int cpu;
>>>>> - xen_hvm_init_shared_info();
>>>>> + if (!suspend_cancelled)
>>>>> + xen_hvm_init_shared_info();
>>>>> xen_callback_vector();
>>>>> xen_unplug_emulated_devices();
>>>>> if (xen_feature(XENFEAT_hvm_safe_pvclock)) {
>>>> Do we need to call other routines if suspend is canceled?
>>>>
>>>> Also, if suspend is canceled then we don't do xen_irq_resume() if that's what you meant by "vcpu_info will be reinitialized". Were you referring some other re-initialization?
>>>>
>>> Hi Boris,
>>>
>>> Sorry I didn't make myself clear.
>>>
>>> About the "vcpu_info reinitialize", I mean in the function "xen_hvm_init_shared_info()" the pointer "xen_vcpu" will be reset and all
>>> point to HYPERVISOR_shared_info->vcpu_info[cpu].
>>>
>>> void __ref xen_hvm_init_shared_info(void)
>>> ----
>>> 1702 * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
>>> 1703 * online but xen_hvm_init_shared_info is run at resume time too and
>>> 1704 * in that case multiple vcpus might be online. */
>>> 1705 for_each_online_cpu(cpu) {
>>> 1706 /* Leave it to be NULL. */
>>> 1707 if (cpu >= MAX_VIRT_CPUS)
>>> 1708 continue;
>>> 1709 per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
>>> 1710 }
>>> 1711 }
>>>
>>>
>>> But on Xen boot the init function "xen_start_kernel" only set the cpu0 to point to HYPERVISOR_shared_info->vcpu_info[0]
>>>
>>> asmlinkage __visible void __init xen_start_kernel(void)
>>
>> We are talking about HVM guests here and xen_start_kernel is only called for PV. But even if it was, xen_vcpu pointers for other VCPUs are set in xen_vcpu_setup(), which is called when non-boot VCPUs are coming up.
>>
>> And I wonder whether the actual problem is that we don't call xen_vcpu_setup() on canceled suspend (as we don't need to, really) and therefore if we call xen_hvm_init_shared_info() then per_cpu(xen_vcpu,cpu) for *non-boot* cpus is will become wrong.
>>
> Yes, you are right, in xen_vcpu_setup() non-boot VCPUs is set to point to xen_vcpu_info
>
> static void xen_vcpu_setup(int cpu)
> ----
> 208 vcpup = &per_cpu(xen_vcpu_info, cpu);
> ...
> 227 /* This cpu is using the registered vcpu info, even if
> 228 later ones fail to. */
> 229 per_cpu(xen_vcpu, cpu) = vcpup;
>
> But on canceled suspend if we call xen_hvm_init_shared_info(), the non-boot VCPUS will be reset to point to HYPERVISOR_shared_info->vcpu_info[cpu] which is a wrong address.
> So I suggest we don't call xen_hvm_init_shared_info() when suspend is canceled.
Right, so can you resubmit the patch with updated commit message? (Just
note there that the hypervisor continues assuming that vcpu_info is
stored in per-cpu data which was set up by xen_vcpu_setup(), while the
call to xen_hvm_init_shared_info() will now make the guest think that
vcpu_info is in the shared page).
Thanks.
-boris
>
>> -boris
>>
>>> ----
>>> 1563 /* Don't do the full vcpu_info placement stuff until we have a
>>> 1564 possible map and a non-dummy shared_info. */
>>> 1565 per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
>>> 1566
>>> 1567 local_irq_disable();
>>>
>>> Other cpus are set to point to "xen_vcpu_info" in function xen_vcpu_setup().
>>>
>>> So after xl save -c/restore, the pointer xen_vcpu will be reset in function "xen_hvm_init_shared_info" and point to a wrong place.
>>> This may cause all the cpus cannot handle irqs except cpu0, so IMHO it's not necessary to call xen_hvm_init_shared_info again if
>>> suspend is canceled.
>>>
>>>> (The patch itself looks like the right thing to do though).
>>>>
>>>> -boris
>>>>
>>>> .
>>>>
>>
>> .
>>
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