linux-kernel - Re: [RFC PATCH 0/7] vfio: Add alias region uapi for device feature

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Message-ID: <CALzav=cuhzsTu7pZSae_6EpbJ1KWq7Th3Puk2n=TEbWN6LWh-g@mail.gmail.com>
Date: Mon, 27 Oct 2025 09:32:17 -0700
From: David Matlack <dmatlack@...gle.com>
To: Mahmoud Adam <mngyadam@...zon.de>
Cc: kvm@...r.kernel.org, jgg@...pe.ca, kbusch@...nel.org, 
	benh@...nel.crashing.org, David Woodhouse <dwmw@...zon.co.uk>, pravkmr@...zon.de, 
	nagy@...aternagy.com, linux-kernel@...r.kernel.org, 
	Alex Williamson <alex@...zbot.org>
Subject: Re: [RFC PATCH 0/7] vfio: Add alias region uapi for device feature

On Wed, Sep 24, 2025 at 7:11 AM Mahmoud Adam <mngyadam@...zon.de> wrote:
>
> This RFC proposes a new uapi VFIO DEVICE_FEATURE to create per-region
> aliases with selectable attributes, initially enabling write-combine
> (WC) where supported by the underlying region. The goal is to expose a
> UAPI for userspace to request an alias of an existing VFIO region with
> extra flags, then interact with it via a stable alias index through
> existing ioctls and mmap where applicable.

Would it make sense to build this on top of Leon's dma-buf series [1]?
My understanding is that dma-buf can support mmap, so WC could just be
a property attached to a dma-buf fd and passed by userspace via
VFIO_DEVICE_FEATURE_DMA_BUF. Then VFIO wouldn't have to create or
manage region aliases.

Apologies if this has already been discussed, I did not go through all
the past discussion.

[1] https://lore.kernel.org/kvm/72ecaa13864ca346797e342d23a7929562788148.1760368250.git.leon@kernel.org/