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From: Jason Gunthorpe <jgg@nvidia.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	ankita@nvidia.com, maz@kernel.org, suzuki.poulose@arm.com,
	yuzenghui@huawei.com, will@kernel.org,
	alex.williamson@redhat.com, kevin.tian@intel.com,
	yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org,
	gshan@redhat.com, linux-mm@kvack.org, aniketa@nvidia.com,
	cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com,
	vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com,
	jhubbard@nvidia.com, danw@nvidia.com, mochs@nvidia.com,
	kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, james.morse@arm.com
Subject: Re: [PATCH v3 2/2] kvm: arm64: set io memory s2 pte as normalnc for vfio pci devices
Date: Mon, 8 Jan 2024 09:18:49 -0400	[thread overview]
Message-ID: <20240108131849.GG50406@nvidia.com> (raw)
In-Reply-To: <ZZvWzyNb1V29-H85@arm.com>

On Mon, Jan 08, 2024 at 11:04:47AM +0000, Catalin Marinas wrote:

> If we want to keep this decision strictly in user space, we can do it
> with some ioctl(). The downside is that the host kernel now puts more
> trust in the user VMM, so my preference would be to keep this in the
> vfio driver. Or we can do both, vfio-pci allows the relaxation, the VMM
> tells KVM to go for a more relaxed stage 2 via an ioctl().

What is the point? We'd need a use case for why the VMM should have
the ability to create a more restrictive MMIO mapping.

I can't think of one.

So I'd go the other way, if someday we find out we need more
restrictive then the VMM should ask for more restrictive (not weirdly
ask for less restrictive)

Jason


WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@nvidia.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	ankita@nvidia.com, maz@kernel.org, suzuki.poulose@arm.com,
	yuzenghui@huawei.com, will@kernel.org,
	alex.williamson@redhat.com, kevin.tian@intel.com,
	yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org,
	gshan@redhat.com, linux-mm@kvack.org, aniketa@nvidia.com,
	cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com,
	vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com,
	jhubbard@nvidia.com, danw@nvidia.com, mochs@nvidia.com,
	kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, james.morse@arm.com
Subject: Re: [PATCH v3 2/2] kvm: arm64: set io memory s2 pte as normalnc for vfio pci devices
Date: Mon, 8 Jan 2024 09:18:49 -0400	[thread overview]
Message-ID: <20240108131849.GG50406@nvidia.com> (raw)
In-Reply-To: <ZZvWzyNb1V29-H85@arm.com>

On Mon, Jan 08, 2024 at 11:04:47AM +0000, Catalin Marinas wrote:

> If we want to keep this decision strictly in user space, we can do it
> with some ioctl(). The downside is that the host kernel now puts more
> trust in the user VMM, so my preference would be to keep this in the
> vfio driver. Or we can do both, vfio-pci allows the relaxation, the VMM
> tells KVM to go for a more relaxed stage 2 via an ioctl().

What is the point? We'd need a use case for why the VMM should have
the ability to create a more restrictive MMIO mapping.

I can't think of one.

So I'd go the other way, if someday we find out we need more
restrictive then the VMM should ask for more restrictive (not weirdly
ask for less restrictive)

Jason


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

  reply	other threads:[~2024-01-08 13:18 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-08 16:47 [PATCH v3 0/2] kvm: arm64: allow vm to select DEVICE_* and ankita
2023-12-08 16:47 ` ankita
2023-12-08 16:47 ` [PATCH v3 1/2] kvm: arm64: introduce new flag for non-cacheable IO memory ankita
2023-12-08 16:47   ` ankita
2023-12-12 12:17   ` Will Deacon
2023-12-12 12:17     ` Will Deacon
2023-12-12 17:31   ` Catalin Marinas
2023-12-12 17:31     ` Catalin Marinas
2024-01-03 11:43   ` Suzuki K Poulose
2024-01-03 11:43     ` Suzuki K Poulose
2024-01-03 13:25     ` Ankit Agrawal
2024-01-03 13:25       ` Ankit Agrawal
2023-12-08 16:47 ` [PATCH v3 2/2] kvm: arm64: set io memory s2 pte as normalnc for vfio pci devices ankita
2023-12-08 16:47   ` ankita
2023-12-12 17:46   ` Catalin Marinas
2023-12-12 17:46     ` Catalin Marinas
2023-12-12 18:11     ` Jason Gunthorpe
2023-12-12 18:11       ` Jason Gunthorpe
2023-12-13 20:05       ` Oliver Upton
2023-12-13 20:05         ` Oliver Upton
2023-12-14 15:48         ` Lorenzo Pieralisi
2023-12-14 15:48           ` Lorenzo Pieralisi
2023-12-14 16:56           ` Oliver Upton
2023-12-14 16:56             ` Oliver Upton
2023-12-21 13:19             ` Catalin Marinas
2023-12-21 13:19               ` Catalin Marinas
2024-01-02 17:09               ` Jason Gunthorpe
2024-01-02 17:09                 ` Jason Gunthorpe
2024-01-03 13:33                 ` Catalin Marinas
2024-01-03 13:33                   ` Catalin Marinas
2024-01-05 20:42               ` Oliver Upton
2024-01-05 20:42                 ` Oliver Upton
2024-01-08 11:04                 ` Catalin Marinas
2024-01-08 11:04                   ` Catalin Marinas
2024-01-08 13:18                   ` Jason Gunthorpe [this message]
2024-01-08 13:18                     ` Jason Gunthorpe
2024-01-02 17:26         ` Jason Gunthorpe
2024-01-02 17:26           ` Jason Gunthorpe

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