linux-kernel - Re: [PATCH] iommu/vt-d: Atomic breakdown of IOPT into finer granularity

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Message-ID: <ZNuM+3R197oRfBer@ziepe.ca>
Date:   Tue, 15 Aug 2023 11:34:35 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jie Ji <jijie.ji@...ux.alibaba.com>
Cc:     dwmw2@...radead.org, baolu.lu@...ux.intel.com, joro@...tes.org,
        will@...nel.org, robin.murphy@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, xianting.tian@...ux.alibaba.com,
        kaijieguo@...ux.alibaba.com, daishengdong@...h.net
Subject: Re: [PATCH] iommu/vt-d: Atomic breakdown of IOPT into finer
 granularity

On Mon, Aug 14, 2023 at 08:10:16PM +0800, Jie Ji wrote:
> With the addition of IOMMU support for IO page fault, it's now possible
> to unpin the memory which DMA remapping. However, the lack of support
> for unmapping a subrange of the I/O page table (IOPT) in IOMMU can lead
> to some issues.
> 
> For instance, a virtual machine can establish IOPT of 2M/1G for better
> performance, while the host system enable swap and attempts to swap out
> some 4K pages. Unfortunately, unmap subrange of the large-page mapping
> will make IOMMU page walk to error level, and finally cause kernel crash.

Nothing in-kernel does something like this.

Jason