Received-SPF: pass (google.com: domain of linux-kernel+bounces-71333-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Mon, 19 Feb 2024 13:40:10 +0100
From: Petr =?UTF-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
To: Will Deacon <will@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
 kernel-team@android.com, iommu@lists.linux.dev, Marek Szyprowski
 <m.szyprowski@samsung.com>, Robin Murphy <robin.murphy@arm.com>, Petr
 Tesarik <petr.tesarik1@huawei-partners.com>, Dexuan Cui
 <decui@microsoft.com>
Subject: Re: [PATCH v3 0/3] Fix double allocation in swiotlb_alloc()
Message-ID: <20240219134010.5b49b8f1@meshulam.tesarici.cz>
In-Reply-To: <20240219092438.GB4105@willie-the-truck>
References: <20240205190127.20685-1-will@kernel.org>
	<20240219063527.GA4580@lst.de>
	<20240219092438.GB4105@willie-the-truck>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Mon, 19 Feb 2024 09:24:39 +0000
Will Deacon <will@kernel.org> wrote:

> Hey Christoph,
> 
> On Mon, Feb 19, 2024 at 07:35:27AM +0100, Christoph Hellwig wrote:
> > Robin and Petr, does this looks good to you now?  

It looks good to me for the boot-time swiotlb pool. Dynamic allocation
of transient swiotlb pools does not take these additional alignment
constraints into account, so when allocation may fail. OTOH the
underlying allocator(s) do not provide a suitable API, so I don't think
it's worth fixing.

In the worst case, a DMA buffer will fail to map, which may already
happen today.

> FWIW, I'm likely to send a v4 addressing another issue reported by
> Nicolin with NVME and 64k pages [1], so you may as well wait for that.

I'm interested. The code look quite OK to me as it is, but I assume it
again uncovers something when the difference between PAGE_SHIFT and
IOTLB_SHIFT is more than one (which was motivation for my initial fix,
which in the end broke more than it fixed).

Petr T