linux-kernel - Re: [PATCH v7 4/4] vfio: convey kvm that the vfio-pci device is wc safe

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Message-ID: <6ab142f0-bf66-4611-915d-938d58a277d3@redhat.com>
Date: Mon, 12 Feb 2024 14:16:30 +0100
From: David Hildenbrand <david@...hat.com>
To: ankita@...dia.com, jgg@...dia.com, maz@...nel.org,
 oliver.upton@...ux.dev, james.morse@....com, suzuki.poulose@....com,
 yuzenghui@...wei.com, reinette.chatre@...el.com, surenb@...gle.com,
 stefanha@...hat.com, brauner@...nel.org, catalin.marinas@....com,
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Cc: aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
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 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 v7 4/4] vfio: convey kvm that the vfio-pci device is wc
 safe

On 11.02.24 18:47, ankita@...dia.com wrote:
> From: Ankit Agrawal <ankita@...dia.com>
> 
> The code to map the MMIO in S2 as NormalNC is enabled when conveyed
> that the device is WC safe using a new flag VM_ALLOW_ANY_UNCACHED.
> 
> Make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag.
> 
> This could be extended to other devices in the future once that
> is deemed safe.

Maybe add some more details how one could make a decision whether it 
would be safe (either here or in patch #2).

> 
> Suggested-by: Catalin Marinas <catalin.marinas@....com>
> Acked-by: Jason Gunthorpe <jgg@...dia.com>
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>   drivers/vfio/pci/vfio_pci_core.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 1cbc990d42e0..eba2146202f9 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1862,8 +1862,12 @@ 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.
> +	 *
> +	 * Set an additional flag VM_ALLOW_ANY_UNCACHED to convey kvm that
> +	 * the device is wc safe.
>   	 */
> -	vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
> +	vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP |
> +			VM_DONTEXPAND | VM_DONTDUMP);
>   	vma->vm_ops = &vfio_pci_mmap_ops;
>   
>   	return 0;

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb