Re: [PATCH] iommu: Always fill in gather when unmapping

From: Jon Hunter <jonathanh@nvidia.com>
To: Jason Gunthorpe <jgg@nvidia.com>, Robin Murphy <robin.murphy@arm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	asahi@lists.linux.dev,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	iommu@lists.linux.dev, Janne Grunau <j@jannau.net>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Joerg Roedel <joro@8bytes.org>,
	Jean-Philippe Brucker <jpb@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-sunxi@lists.linux.dev,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Neal Gompa <neal@gompa.dev>, Orson Zhai <orsonzhai@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <pjw@kernel.org>,
	Samuel Holland <samuel@sholland.org>,
	Sven Peter <sven@kernel.org>,
	virtualization@lists.linux.dev, Chen-Yu Tsai <wens@kernel.org>,
	Will Deacon <will@kernel.org>, Yong Wu <yong.wu@mediatek.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>,
	Joerg Roedel <joerg.roedel@amd.com>,
	patches@lists.linux.dev, Samiullah Khawaja <skhawaja@google.com>,
	stable@vger.kernel.org, Vasant Hegde <vasant.hegde@amd.com>,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
Subject: Re: [PATCH] iommu: Always fill in gather when unmapping
Date: Wed, 8 Apr 2026 14:34:59 +0100	[thread overview]
Message-ID: <56559431-b73b-4e3b-8554-7a72d78e2b67@nvidia.com> (raw)
In-Reply-To: <94576121-d4ff-47fd-9ff8-2a00ff4c5c2a@nvidia.com>

On 08/04/2026 09:42, Jon Hunter wrote:
> Hi Robin, Jason,
> 
> On 02/04/2026 23:51, Jason Gunthorpe wrote:
>> On Thu, Apr 02, 2026 at 07:11:13PM +0100, Robin Murphy wrote:
>>>>> @@ -2714,6 +2714,10 @@ static size_t __iommu_unmap(struct 
>>>>> iommu_domain *domain,
>>>>>            pr_debug("unmapped: iova 0x%lx size 0x%zx\n",
>>>>>                 iova, unmapped_page);
>>>>> +        /* If the driver itself isn't using the gather, mark it 
>>>>> used */
>>>>> +        if (iotlb_gather->end <= iotlb_gather->start)
>>>>> +            iommu_iotlb_gather_add_range(&iotlb_gather, iova, 
>>>>> unmapped_page);
>>>>
>>>> The gathers can be joined across unmaps and now we are inviting subtly
>>>> ill-formed gathers as only the first unmap will get included.
>>
>>>> We do have error cases where the gather is legitimately empty, and
>>>> this would squash that, it probably needs to check unmapped_page for 0
>>>> too, at least.
>>>
>>> Maybe try looking at the rest of the code around these lines...
>>
>> Okay, well lets do this one, do you want to send it since it is your
>> idea?
> 
> 
> Any update on this? Boot is still broken on a couple of our boards.

I just noticed that this is now broken on mainline as well as -next. Can 
we get a fix in place before v7.0 is released?

Thanks
Jon

-- 
nvpublic