Messages in this thread | | | Date | Thu, 30 Apr 2015 15:27:14 +0800 | From | "Ouyang Zhaowei (Charles)" <> | Subject | Re: [PATCH] xen: vcpu_info reinit error after 'xl save -c' & 'xl restore' on PVOPS VM which has multi-cpu |
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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@huawei.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.
> -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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