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Date: Wed, 11 Jun 2025 14:00:04 -0600
From: Keith Busch <kbusch@kernel.org>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Sagi Grimberg <sagi@grimberg.me>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Kanchan Joshi <joshi.k@samsung.com>,
	Leon Romanovsky <leon@kernel.org>,
	Nitesh Shetty <nj.shetty@samsung.com>, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org
Subject: Re: [PATCH 1/9] block: don't merge different kinds of P2P transfers
 in a single bio
Message-ID: <aEngRKqXEYmikcn2@kbusch-mbp>
References: <20250610050713.2046316-1-hch@lst.de>
 <20250610050713.2046316-2-hch@lst.de>
 <aEhROl2D89kFX8C7@kbusch-mbp>
 <20250611034316.GA2869@lst.de>
 <aEmuG1dUDGuci7VW@kbusch-mbp>
 <5cddbda3-02bd-4dc1-9f7f-197279da6279@deltatee.com>
 <aEmxn0K6m34HsZeN@kbusch-mbp>
 <88fe6154-6086-409d-a180-665d62d72d47@deltatee.com>
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In-Reply-To: <88fe6154-6086-409d-a180-665d62d72d47@deltatee.com>

On Wed, Jun 11, 2025 at 01:41:54PM -0600, Logan Gunthorpe wrote:
> On 2025-06-11 10:41, Keith Busch wrote:
> > Is there some other mechansim that ensures a host memory mapped IOVA
> > doesn't collide with a PCI bus address then?
> 
> Yes, in the absence of a switch with ACS protection this can be a problem.
> 
> I haven't looked at this in a long time, but the iommu drivers reserve
> regions where the PCI addresses are valid so no iova will be allocated
> with a similar bus address. After a quick search, I believe today, this
> is handled by iova_reserve_pci_windows().

Excellent, I think that was the piece I was missing. Thanks!