From: Christoph Hellwig <hch@lst.de>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: alan.cox@intel.com, Christoph Hellwig <hch@lst.de>,
Stefano Stabellini <sstabellini@kernel.org>,
ashok.raj@intel.com, Jonathan Corbet <corbet@lwn.net>,
pengfei.xu@intel.com, Ingo Molnar <mingo@redhat.com>,
David Woodhouse <dwmw2@infradead.org>,
kevin.tian@intel.com,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Steven Rostedt <rostedt@goodmis.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
mika.westerberg@linux.intel.com, Juergen Gross <jgross@suse.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
jacob.jun.pan@intel.com, Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops
Date: Thu, 25 Jul 2019 13:43:48 +0200 [thread overview]
Message-ID: <20190725114348.GA30957@lst.de> (raw)
In-Reply-To: <bc831f88-5b19-7531-00aa-a7577dd5c1ac@linux.intel.com>
On Thu, Jul 25, 2019 at 03:18:03PM +0800, Lu Baolu wrote:
>> Don't we need to keep this bit so that we still allow the IOMMU
>> to act if the device has a too small DMA mask to address all memory in
>> the system, even if if it should otherwise be identity mapped?
>>
>
> This checking happens only when device is using an identity mapped
> domain. If the device has a small DMA mask, swiotlb will be used for
> high memory access.
>
> This is supposed to be handled in dma_direct_map_page():
>
> if (unlikely(!dma_direct_possible(dev, dma_addr, size)) &&
> !swiotlb_map(dev, &phys, &dma_addr, size, dir, attrs)) {
> report_addr(dev, dma_addr, size);
> return DMA_MAPPING_ERROR;
> }
Well, yes. But the point is that the current code uses dynamic iommu
mappings even if the devices is in the identity mapped domain when the
dma mask іs too small to map all memory directly. Your change means it
will now use swiotlb which is most likely going to be a lot more
expensive. I don't think that this change is a good idea, and even if
we decide that this is a good idea after all that should be done in a
separate prep patch that explains the rationale.
> Best regards,
> Baolu
---end quoted text---
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next prev parent reply other threads:[~2019-07-25 11:43 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-25 3:17 [PATCH v5 00/10] iommu: Bounce page for untrusted devices Lu Baolu
2019-07-25 3:17 ` [PATCH v5 01/10] iommu/vt-d: Don't switch off swiotlb if use direct dma Lu Baolu
2019-07-25 5:41 ` Christoph Hellwig
2019-07-25 3:17 ` [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops Lu Baolu
2019-07-25 5:44 ` Christoph Hellwig
2019-07-25 7:18 ` Lu Baolu
2019-07-25 11:43 ` Christoph Hellwig [this message]
2019-07-26 1:56 ` Lu Baolu
2019-11-12 7:16 ` Christoph Hellwig
2019-11-13 2:50 ` Lu Baolu
2019-11-13 7:03 ` Christoph Hellwig
2019-11-13 9:53 ` Christoph Hellwig
2019-11-14 5:14 ` Lu Baolu
2019-11-14 8:14 ` Christoph Hellwig
2019-07-25 3:17 ` [PATCH v5 03/10] iommu/vt-d: Cleanup after use per-device dma ops Lu Baolu
2019-07-25 3:17 ` [PATCH v5 04/10] PCI: Add dev_is_untrusted helper Lu Baolu
2019-07-25 5:44 ` Christoph Hellwig
2019-07-25 3:17 ` [PATCH v5 05/10] swiotlb: Split size parameter to map/unmap APIs Lu Baolu
2019-07-25 11:47 ` Christoph Hellwig
2019-07-25 3:17 ` [PATCH v5 06/10] swiotlb: Zero out bounce buffer for untrusted device Lu Baolu
2019-07-25 11:49 ` Christoph Hellwig
2019-07-26 2:21 ` Lu Baolu
2019-07-25 3:17 ` [PATCH v5 07/10] iommu: Add bounce page APIs Lu Baolu
2019-07-25 3:17 ` [PATCH v5 08/10] iommu/vt-d: Check whether device requires bounce buffer Lu Baolu
2019-07-25 3:17 ` [PATCH v5 09/10] iommu/vt-d: Add trace events for device dma map/unmap Lu Baolu
2019-07-25 12:26 ` Steven Rostedt
2019-07-26 2:24 ` Lu Baolu
2019-07-25 3:17 ` [PATCH v5 10/10] iommu/vt-d: Use bounce buffer for untrusted devices Lu Baolu
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