linux-kernel - Re: [PATCH] KVM: arm64: nv: Forward hvc traps if originated from nested VM

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Message-ID: <4d1bdea5-43c3-4ca9-9275-feadf158e86e@os.amperecomputing.com>
Date: Thu, 10 Apr 2025 15:50:24 +0530
From: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 linux-kernel@...r.kernel.org, oliver.upton@...ux.dev, joey.gouly@....com,
 suzuki.poulose@....com, yuzenghui@...wei.com, darren@...amperecomputing.com
Subject: Re: [PATCH] KVM: arm64: nv: Forward hvc traps if originated from
 nested VM



On 10-04-2025 12:49 pm, Marc Zyngier wrote:
> On Thu, 10 Apr 2025 08:07:43 +0100,
> Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com> wrote:
>>
>> It was discovered while trying selftest(smccc_filter) that the
>> hvc trap is getting forwarded to guest hypervisor even if it is
>> originated from itself.
>>
>> HVC traps from guest hypervisor should be handled by the host
>> hypervisor and traps originating from nested VM should be
>> forwarded. Adding check to forward only if the hvc is trapped
>> from the nested VM.
> 
> I disagree. HVC from EL2 must be routed to the same EL2. HVC from EL1
> must be routed to the EL2 controlling EL1.

Thanks, Understood, In NV case, hvc has to be forwarded to L1 
irrespective of it origin (L1 or L2). Need to add hvc handler in the 
smccc_filter.c for the vm (when run as L1), so that it is handled and 
returns with required args set.


-- 
Thanks,
Ganapat/GK