linux-kernel - Re: [RFC PATCH v2 0/9] KVM: Enable Nested Virt selftests

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Message-ID: <9d5d82f1-b488-4b0a-98c2-27e95d63fc5c@os.amperecomputing.com>
Date: Mon, 23 Jun 2025 16:01:32 +0530
From: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
To: Marc Zyngier <maz@...nel.org>
Cc: Eric Auger <eauger@...hat.com>, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, oliver.upton@...ux.dev, joey.gouly@....com,
 suzuki.poulose@....com, yuzenghui@...wei.com, seanjc@...gle.com,
 darren@...amperecomputing.com
Subject: Re: [RFC PATCH v2 0/9] KVM: Enable Nested Virt selftests

On 6/19/2025 5:15 PM, Marc Zyngier wrote:
>>   >
>>> Also, running EL2 is the least of our worries, because that's pretty
>>> easy to deal with. It is running at EL1/0 when EL2 is present that is
>>> interesting, and I see no coverage on that front.
>>
>> Sorry, I did not get this comment fully.
>> When we run selftest on Host with -g option, the guest code will run in vEL2 as L1.
>> This is implemented as per comment in V1.
>>
>> When we run same selftest from L1 shell, then guest_code will be running in EL0/1 like running from L0.
> 
> What good does this bring us if we need to boot a full guest OS to run
> tests? What we need is synthetic tests that implement the whole stack:
> 
> - L1 guest hypervisor
> - L2 guest hypervisor
> - L2 guest
> - L3 guest hypervisor
> - L3 guest
> - [...]

IIUC, selftest leverages host OS support and uses various IOCTLs to support the guest_code run. Are you saying to implement all this again (without OS help) in guest_code to run it as hypervisor and launch guest_code2 as NestedVM?. It seems to be complicated, doesn't it?

> 
> This is *one* test. Not a test that runs in a guest. That's what I've
> been asking since day one.
-- 
Thanks,
Gk