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From: Marc Zyngier <maz@kernel.org>
To: Shenming Lu <lushenming@huawei.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	kvm@vger.kernel.org, Cornelia Huck <cohuck@redhat.com>,
	linux-kernel@vger.kernel.org,
	Alex Williamson <alex.williamson@redhat.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 2/4] KVM: arm64: GICv4.1: Try to save hw pending state in save_pending_tables
Date: Fri, 12 Mar 2021 09:02:58 +0000	[thread overview]
Message-ID: <87lfasg2wt.wl-maz@kernel.org> (raw)
In-Reply-To: <3b47598f-0795-a165-1a64-abe02258b306@huawei.com>

On Thu, 11 Mar 2021 12:31:48 +0000,
Shenming Lu <lushenming@huawei.com> wrote:
> 
> On 2021/3/11 17:09, Marc Zyngier wrote:

> > I have asked that question in the past: is it actually safe to remap
> > the vPEs and expect them to be runnable
> 
> In my opinion, logically it can work, but there might be problems like the
> one below that I didn't notice...

One thing is that you will have lost interrupts in the meantime
(assuming your devices are still alive). How will you make up for
that?

> 
> > 
> > Also, the current code assumes that VMAPP.PTZ can be advertised if a
> > VPT is mapped for the first time. Clearly, it is unlikely that the VPT
> > will be only populated with 0s, so you'll end up with state corruption
> > on the first remap.
> 
> Oh, thanks for pointing it out.
> And if we always signal PTZ when alloc = 1, does it mean that we
> can't remap the vPE when the VPT is not empty, thus there is no
> chance to get the VLPI state?  Could we just assume that the VPT is
> not empty when first mapping the vPE?

I think we should drop the setting of PTZ altogether. It is a silly
micro-optimisation, and if the HW can't parse the VPT efficiently when
it is empty, then the HW is pretty bad, PTZ or not.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Shenming Lu <lushenming@huawei.com>
Cc: Eric Auger <eric.auger@redhat.com>, Will Deacon <will@kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<kvmarm@lists.cs.columbia.edu>, <kvm@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	"Lorenzo\ Pieralisi" <lorenzo.pieralisi@arm.com>,
	<wanghaibin.wang@huawei.com>, <yuzenghui@huawei.com>
Subject: Re: [PATCH v3 2/4] KVM: arm64: GICv4.1: Try to save hw pending state in save_pending_tables
Date: Fri, 12 Mar 2021 09:02:58 +0000	[thread overview]
Message-ID: <87lfasg2wt.wl-maz@kernel.org> (raw)
In-Reply-To: <3b47598f-0795-a165-1a64-abe02258b306@huawei.com>

On Thu, 11 Mar 2021 12:31:48 +0000,
Shenming Lu <lushenming@huawei.com> wrote:
> 
> On 2021/3/11 17:09, Marc Zyngier wrote:

> > I have asked that question in the past: is it actually safe to remap
> > the vPEs and expect them to be runnable
> 
> In my opinion, logically it can work, but there might be problems like the
> one below that I didn't notice...

One thing is that you will have lost interrupts in the meantime
(assuming your devices are still alive). How will you make up for
that?

> 
> > 
> > Also, the current code assumes that VMAPP.PTZ can be advertised if a
> > VPT is mapped for the first time. Clearly, it is unlikely that the VPT
> > will be only populated with 0s, so you'll end up with state corruption
> > on the first remap.
> 
> Oh, thanks for pointing it out.
> And if we always signal PTZ when alloc = 1, does it mean that we
> can't remap the vPE when the VPT is not empty, thus there is no
> chance to get the VLPI state?  Could we just assume that the VPT is
> not empty when first mapping the vPE?

I think we should drop the setting of PTZ altogether. It is a silly
micro-optimisation, and if the HW can't parse the VPT efficiently when
it is empty, then the HW is pretty bad, PTZ or not.

Thanks,

	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

  reply	other threads:[~2021-03-12  9:03 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 12:13 [PATCH v3 0/4] KVM: arm64: Add VLPI migration support on GICv4.1 Shenming Lu
2021-01-27 12:13 ` Shenming Lu
2021-01-27 12:13 ` Shenming Lu
2021-01-27 12:13 ` [PATCH v3 1/4] KVM: arm64: GICv4.1: Add function to get VLPI state Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-03-11  8:57   ` Marc Zyngier
2021-03-11  8:57     ` Marc Zyngier
2021-03-11 12:26     ` Shenming Lu
2021-03-11 12:26       ` Shenming Lu
2021-03-11 12:26       ` Shenming Lu
2021-03-12  8:52       ` Marc Zyngier
2021-03-12  8:52         ` Marc Zyngier
2021-01-27 12:13 ` [PATCH v3 2/4] KVM: arm64: GICv4.1: Try to save hw pending state in save_pending_tables Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-03-11  9:09   ` Marc Zyngier
2021-03-11  9:09     ` Marc Zyngier
2021-03-11 12:31     ` Shenming Lu
2021-03-11 12:31       ` Shenming Lu
2021-03-11 12:31       ` Shenming Lu
2021-03-12  9:02       ` Marc Zyngier [this message]
2021-03-12  9:02         ` Marc Zyngier
2021-03-12 10:47         ` Shenming Lu
2021-03-12 10:47           ` Shenming Lu
2021-03-12 10:47           ` Shenming Lu
2021-01-27 12:13 ` [PATCH v3 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-03-11  9:14   ` Marc Zyngier
2021-03-11  9:14     ` Marc Zyngier
2021-03-11 12:32     ` Shenming Lu
2021-03-11 12:32       ` Shenming Lu
2021-03-11 12:32       ` Shenming Lu
2021-03-12  9:05       ` Marc Zyngier
2021-03-12  9:05         ` Marc Zyngier
2021-03-12 10:48         ` Shenming Lu
2021-03-12 10:48           ` Shenming Lu
2021-03-12 10:48           ` Shenming Lu
2021-03-12 11:10           ` Marc Zyngier
2021-03-12 11:10             ` Marc Zyngier
2021-03-12 11:34             ` Shenming Lu
2021-03-12 11:34               ` Shenming Lu
2021-03-12 11:34               ` Shenming Lu
2021-03-12 12:02               ` Marc Zyngier
2021-03-12 12:02                 ` Marc Zyngier
2021-03-12 12:31                 ` Shenming Lu
2021-03-12 12:31                   ` Shenming Lu
2021-03-12 12:31                   ` Shenming Lu
2021-01-27 12:13 ` [PATCH v3 4/4] KVM: arm64: GICv4.1: Give a chance to save VLPI's pending state Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-01-27 12:13   ` Shenming Lu
2021-02-26  8:58 ` [PATCH v3 0/4] KVM: arm64: Add VLPI migration support on GICv4.1 Shenming Lu
2021-02-26  8:58   ` Shenming Lu
2021-02-26  8:58   ` Shenming Lu
2021-03-11  7:03   ` Shenming Lu
2021-03-11  7:03     ` Shenming Lu
2021-03-11  7:03     ` Shenming Lu
2021-03-11  9:17     ` Marc Zyngier
2021-03-11  9:17       ` Marc Zyngier

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