linux-kernel - Re: [PATCH 2/2] KVM: X86: Implement PV send IPI support

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Date:   Fri, 29 Jun 2018 12:48:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 2/2] KVM: X86: Implement PV send IPI support

On 29/06/2018 12:09, Vitaly Kuznetsov wrote:
>> +KVM_FEATURE_PV_SEND_IPI            ||    11 || guest checks this feature bit
>> +                                   ||       || before enabling paravirtualized
>> +                                   ||       || send IPIs.
> In case we decide to apply this as-is we'll likely need a new feature
> for PV IPI with > 64 vCPUs (or how else would the guest know if the host
> is capable or not?)
> 

Yes, it makes sense.  Perhaps we can do one of the following, or both:

1) add an argument for a "base vCPU id", so that you can use the
hypercall to send the IPI to CPUs 64..127, 128..191 etc.

2) have two bitmask arguments so that one hypercall handles 128 vCPUs.

to remove or limit the need for the more generic hypercall.

Paolo