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From: Marc Zyngier <maz@kernel.org>
To: Cornelia Huck <cohuck@redhat.com>
Cc: Jianyong Wu <jianyong.wu@arm.com>,
	james.morse@arm.com, will@kernel.org, rmk@armlinux.org.uk,
	salil.mehta@huawei.com, suzuki.poulose@arm.com,
	oliver.upton@linux.dev, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org,
	justin.he@arm.com
Subject: Re: [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter
Date: Thu, 16 Nov 2023 14:21:37 +0000	[thread overview]
Message-ID: <8634x522z2.wl-maz@kernel.org> (raw)
In-Reply-To: <877cmhq1zp.fsf@redhat.com>

On Thu, 16 Nov 2023 13:08:58 +0000,
Cornelia Huck <cohuck@redhat.com> wrote:
> 
> On Thu, Nov 16 2023, Jianyong Wu <jianyong.wu@arm.com> wrote:
> 
> > 821d935c87b introduces support for userspace SMCCC filtering, but lack
> > of a way to tell userspace if we have this feature. Add a corresponding
> > feature extension can resolve this issue.
> >
> > For example, the incoming feature Vcpu Hotplug needs the SMCCC filter.
> > As there is no way to check this feature, VMM will run into error when
> > it calls this feature on an old kernel. It's bad for backward compatible.
> 
> Can't you simply query via KVM_HAS_DEVICE_ATTR whether the SMCCC
> filtering controls exist?

Quite. Commit e0fc6b21616dd introduced it for that exact purpose,
specifically to prevent adding more of these capabilities when there
is a corresponding attribute that can be readily queried.

	M.

-- 
Without deviation from the norm, progress is not possible.

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Cornelia Huck <cohuck@redhat.com>
Cc: Jianyong Wu <jianyong.wu@arm.com>,
	james.morse@arm.com, will@kernel.org, rmk@armlinux.org.uk,
	salil.mehta@huawei.com, suzuki.poulose@arm.com,
	oliver.upton@linux.dev, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org,
	justin.he@arm.com
Subject: Re: [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter
Date: Thu, 16 Nov 2023 14:21:37 +0000	[thread overview]
Message-ID: <8634x522z2.wl-maz@kernel.org> (raw)
In-Reply-To: <877cmhq1zp.fsf@redhat.com>

On Thu, 16 Nov 2023 13:08:58 +0000,
Cornelia Huck <cohuck@redhat.com> wrote:
> 
> On Thu, Nov 16 2023, Jianyong Wu <jianyong.wu@arm.com> wrote:
> 
> > 821d935c87b introduces support for userspace SMCCC filtering, but lack
> > of a way to tell userspace if we have this feature. Add a corresponding
> > feature extension can resolve this issue.
> >
> > For example, the incoming feature Vcpu Hotplug needs the SMCCC filter.
> > As there is no way to check this feature, VMM will run into error when
> > it calls this feature on an old kernel. It's bad for backward compatible.
> 
> Can't you simply query via KVM_HAS_DEVICE_ATTR whether the SMCCC
> filtering controls exist?

Quite. Commit e0fc6b21616dd introduced it for that exact purpose,
specifically to prevent adding more of these capabilities when there
is a corresponding attribute that can be readily queried.

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2023-11-16 14:21 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-16 11:41 [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter Jianyong Wu
2023-11-16 11:41 ` Jianyong Wu
2023-11-16 13:08 ` Cornelia Huck
2023-11-16 13:08   ` Cornelia Huck
2023-11-16 14:06   ` Salil Mehta
2023-11-16 14:06     ` Salil Mehta
2023-11-21  1:58     ` Jianyong Wu
2023-11-21  1:58       ` Jianyong Wu
2023-11-16 14:21   ` Marc Zyngier [this message]
2023-11-16 14:21     ` Marc Zyngier
2023-11-21  2:01     ` Jianyong Wu
2023-11-21  2:01       ` Jianyong Wu
2023-11-16 19:06 ` Russell King (Oracle)
2023-11-16 19:06   ` Russell King (Oracle)
2023-11-16 23:22   ` Oliver Upton
2023-11-16 23:22     ` Oliver Upton
2023-11-21 10:57     ` Salil Mehta
2023-11-21 10:57       ` Salil Mehta

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