linux-kernel - Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL

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Date:   Tue, 5 Dec 2023 18:40:42 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Jason Gunthorpe <jgg@...dia.com>, ankita@...dia.com,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>, oliver.upton@...ux.dev,
        suzuki.poulose@....com, yuzenghui@...wei.com, will@...nel.org,
        ardb@...nel.org, akpm@...ux-foundation.org, gshan@...hat.com,
        aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
        targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
        apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
        mochs@...dia.com, kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
        lpieralisi@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and
 NORMAL_NC for IO memory

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@....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