Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Date:   Tue, 5 Dec 2023 18:40:42 +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
Message-ID: <ZW9uqu7yOtyZfmvC@arm.com>
References: <20231205033015.10044-1-ankita@nvidia.com>
 <86fs0hatt3.wl-maz@kernel.org>
 <ZW8MP2tDt4_9ROBz@arm.com>
 <20231205130517.GD2692119@nvidia.com>
 <ZW9OSe8Z9gAmM7My@arm.com>
 <20231205164318.GG2692119@nvidia.com>
 <86bkb4bn2v.wl-maz@kernel.org>
 <ZW9ezSGSDIvv5MsQ@arm.com>
 <86a5qobkt8.wl-maz@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <86a5qobkt8.wl-maz@kernel.org>
Precedence: bulk

On Tue, Dec 05, 2023 at 05:50:27PM +0000, Marc Zyngier wrote:
> On Tue, 05 Dec 2023 17:33:01 +0000,
> Catalin Marinas <catalin.marinas@arm.com> wrote:
> > Ideally we should do this for vfio only but we don't have an easy
> > way to convey this to KVM.
> 
> But if we want to limit this to PCIe, we'll have to find out. The
> initial proposal (a long while ago) had a flag conveying some
> information, and I'd definitely feel more confident having something
> like that.

We can add a VM_PCI_IO in the high vma flags to be set by
vfio_pci_core_mmap(), though it limits it to 64-bit architectures. KVM
knows this is PCI and relaxes things a bit. It's not generic though if
we need this later for something else.

A question for Lorenzo: do these BARs appear in iomem_resource? We could
search that up instead of a flag, something like the page_is_ram()
helper.

-- 
Catalin