linux-kernel - Re: KVM: arm64: vgic-its: Return -ENXIO to invalid KVM_DEV_ARM_VGIC_GRP

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Message-ID: <0f86df0c2866114898da1e9f4274e23b3d1c38b4.camel@infradead.org>
Date: Tue, 24 Jun 2025 11:01:38 +0200
From: David Woodhouse <dwmw2@...radead.org>
To: Eric Auger <eauger@...hat.com>, Marc Zyngier <maz@...nel.org>, Oliver
 Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>, Suzuki K
 Poulose <suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Jing Zhang <jingzhangos@...gle.com>, Kunkun Jiang <jiangkunkun@...wei.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Sebastian Ott <sebott@...hat.com>,
 Maxim Levitsky <mlevitsk@...hat.com>, Keisuke Nishimura
 <keisuke.nishimura@...ia.fr>,  linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev,  linux-kernel@...r.kernel.org
Subject: Re: KVM: arm64: vgic-its: Return -ENXIO to invalid
 KVM_DEV_ARM_VGIC_GRP_CTRL attrs

On Tue, 2025-06-24 at 09:25 +0200, Eric Auger wrote:
> Hi David,
> 
> On 6/23/25 3:22 PM, David Woodhouse wrote:
> > From: David Woodhouse <dwmw@...zon.co.uk>
> > 
> > A preliminary version of a hack to invoke unmap_all_vpes() from an ioctl
> > didn't work very well. We eventually determined this was because we were
> > invoking it on the wrong file descriptor, but not getting an error.
> > 
> > Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
>
> In the corresponding doc (virt/kvm/devices/arm-vgic-its.rst)
> it is said about possible returned values:
>      -ENXIO  ITS not properly configured as required prior to setting
>              this attribute
> which does not exactly match your situation. Shouldn't we also update
> the doc or change the returned value?

Hi Eric, thanks for looking at this.

I think this is OK because the -ENXIO return is covered by the high-
level description of KVM_[GS]ET_DEVICE_ATTR in virt/kvm/api.rst:

Errors:

  =====   =============================================================
  ENXIO   The group or attribute is unknown/unsupported for this device
          or hardware support is missing.


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