linux-kernel - Re: [PATCH v8 4/4] vfio: convey kvm that the vfio-pci device is wc safe

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Message-ID: <ZdR3MI_4pqV0EZcR@arm.com>
Date: Tue, 20 Feb 2024 09:56:00 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: ankita@...dia.com
Cc: jgg@...dia.com, maz@...nel.org, oliver.upton@...ux.dev,
	james.morse@....com, suzuki.poulose@....com, yuzenghui@...wei.com,
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	apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
	kvmarm@...ts.linux.dev, mochs@...dia.com, zhiw@...dia.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 4/4] vfio: convey kvm that the vfio-pci device is wc
 safe

On Tue, Feb 20, 2024 at 12:59:26PM +0530, ankita@...dia.com wrote:
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 1cbc990d42e0..c93bea18fc4b 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1862,8 +1862,24 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
>  	/*
>  	 * See remap_pfn_range(), called from vfio_pci_fault() but we can't
>  	 * change vm_flags within the fault handler.  Set them now.
> +	 *
> +	 * VM_ALLOW_ANY_UNCACHED: The VMA flag is implemented for ARM64,
> +	 * allowing KVM stage 2 device mapping attributes to use Normal-NC
> +	 * rather than DEVICE_nGnRE, which allows guest mappings
> +	 * supporting combining attributes (WC). ARM does not

Nitpick: "supporting write-combining" (if you plan to respin).

-- 
Catalin