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Re: [Qemu-arm] [PATCH v6 2/2] target: arm: Add support for VCPU event st
From: |
gengdongjiu |
Subject: |
Re: [Qemu-arm] [PATCH v6 2/2] target: arm: Add support for VCPU event states |
Date: |
Fri, 24 Aug 2018 18:49:39 +0800 |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
On 2018/8/24 18:38, Peter Maydell wrote:
> On 24 August 2018 at 11:28, gengdongjiu <address@hidden> wrote:
>> On 2018/8/24 0:52, Peter Maydell wrote:
>>> On 23 August 2018 at 16:45, Dongjiu Geng <address@hidden> wrote:
>>>> +static int kvm_put_vcpu_events(ARMCPU *cpu)
>>>> +{
>>>> + CPUARMState *env = &cpu->env;
>>>> + struct kvm_vcpu_events events = {};
>>>> +
>>>> + if (!kvm_has_vcpu_events()) {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + memset(&events, 0, sizeof(events));
>>>> + events.exception.serror_pending = env->serror.pending;
>>>> +
>>>> + if (have_inject_serror_esr) {
>>>> + events.exception.serror_has_esr = env->serror.has_esr;
>>>> + events.exception.serror_esr = env->serror.esr;
>>>> + }
>>>
>>> I realised that the effect of this condition is that
>>> if we migrate a VM from a machine which supports specifying the
>>> SError ESR to one which does not, and at the point of migration
>>> there is a pending SError with an ESR value, then we will
>>> silently drop the specified ESR value. The other alternative
>>> would be to fail the migration (by dropping the if() check,
>>> and letting the host kernel fail the ioctl if that meant that
>>> we asked it to set an SError ESR it couldn't manage.)
>>>
>>> I guess that's OK? It's all hypothetical currently since
>>> we don't support migration between different host CPU types.
>>
>> Peter,
>> there are two status needed to migrate, one is serror_pending, another is
>> SError ESR value.
>>
>> If A migrates to B, A can set an SError ESR, but B does not support to set.
>> when A is pending a SError and need to migrate to B, I think it should
>> support to migrate the serror_pending status without the ESR value(the ESR
>> value is 0).
>> That is to say, if A is pending a SError, when migrate to B, B should also
>> pend a SError.
>>
>> or do you think we should refused this migration?
>
> I don't know, that's why I asked. If we have a pending
> SError with an ESR, and we end up on a destination machine
> where we can pend the SError but not the ESR, does that
> make sense (ie will the guest still be able to usefully
I agree this suggestion that can pend the SError but without the ESR in the
destination machine.
> continue), or have we thrown away information that the
> guest requires to be able to usefully use the SError ?
> Presumably the ESR is important, or we could just never
> bother to set it when pending SErrors.
>
> thanks
> -- PMM
>
> .
>