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Date:   Tue, 5 Dec 2023 17:33:01 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     Jason Gunthorpe <jgg@nvidia.com>, ankita@nvidia.com,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@huawei.com>, oliver.upton@linux.dev,
        suzuki.poulose@arm.com, yuzenghui@huawei.com, will@kernel.org,
        ardb@kernel.org, akpm@linux-foundation.org, gshan@redhat.com,
        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,
        lpieralisi@kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and
 NORMAL_NC for IO memory
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On Tue, Dec 05, 2023 at 05:01:28PM +0000, Marc Zyngier wrote:
> On Tue, 05 Dec 2023 16:43:18 +0000,
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> > On Tue, Dec 05, 2023 at 04:22:33PM +0000, Catalin Marinas wrote:
> > > That's an argument to restrict this feature to PCIe. It's really about
> > > fewer arguments on the behaviour of other devices. Marc did raise
> > > another issue with the GIC VCPU interface (does this even have a vma in
> > > the host VMM?). That's a class of devices where the mapping is
> > > context-switched, so the TLBI+DSB rules don't help.
> 
> There is no vma. The CPU interface is entirely under control of KVM.
> Userspace only provides the IPA for the mapping.

That's good to know. We can solve the GIC issue by limiting the
relaxation to those mappings that have a user vma. Ideally we should do
this for vfio only but we don't have an easy way to convey this to KVM.

-- 
Catalin