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From: Robin Murphy <robin.murphy@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Joerg Roedel <joro@8bytes.org>,
	Li Yang <leoyang.li@nxp.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, linux-arm-msm@vger.kernel.org,
	dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
	iommu@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH 16/18] iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE
Date: Tue, 30 Mar 2021 17:28:19 +0100	[thread overview]
Message-ID: <578d6aa5-4239-f5d7-2e9f-686b18e52bba@arm.com> (raw)
In-Reply-To: <20210330135801.GA6187@willie-the-truck>

On 2021-03-30 14:58, Will Deacon wrote:
> On Tue, Mar 30, 2021 at 02:19:38PM +0100, Robin Murphy wrote:
>> On 2021-03-30 14:11, Will Deacon wrote:
>>> On Tue, Mar 16, 2021 at 04:38:22PM +0100, Christoph Hellwig wrote:
>>>> From: Robin Murphy <robin.murphy@arm.com>
>>>>
>>>> Instead make the global iommu_dma_strict paramete in iommu.c canonical by
>>>> exporting helpers to get and set it and use those directly in the drivers.
>>>>
>>>> This make sure that the iommu.strict parameter also works for the AMD and
>>>> Intel IOMMU drivers on x86.  As those default to lazy flushing a new
>>>> IOMMU_CMD_LINE_STRICT is used to turn the value into a tristate to
>>>> represent the default if not overriden by an explicit parameter.
>>>>
>>>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>.
>>>> [ported on top of the other iommu_attr changes and added a few small
>>>>    missing bits]
>>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>>> ---
>>>>    drivers/iommu/amd/iommu.c                   | 23 +-------
>>>>    drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 50 +---------------
>>>>    drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 -
>>>>    drivers/iommu/arm/arm-smmu/arm-smmu.c       | 27 +--------
>>>>    drivers/iommu/dma-iommu.c                   |  9 +--
>>>>    drivers/iommu/intel/iommu.c                 | 64 ++++-----------------
>>>>    drivers/iommu/iommu.c                       | 27 ++++++---
>>>>    include/linux/iommu.h                       |  4 +-
>>>>    8 files changed, 40 insertions(+), 165 deletions(-)
>>>
>>> I really like this cleanup, but I can't help wonder if it's going in the
>>> wrong direction. With SoCs often having multiple IOMMU instances and a
>>> distinction between "trusted" and "untrusted" devices, then having the
>>> flush-queue enabled on a per-IOMMU or per-domain basis doesn't sound
>>> unreasonable to me, but this change makes it a global property.
>>
>> The intent here was just to streamline the existing behaviour of stuffing a
>> global property into a domain attribute then pulling it out again in the
>> illusion that it was in any way per-domain. We're still checking
>> dev_is_untrusted() before making an actual decision, and it's not like we
>> can't add more factors at that point if we want to.
> 
> Like I say, the cleanup is great. I'm just wondering whether there's a
> better way to express the complicated logic to decide whether or not to use
> the flush queue than what we end up with:
> 
> 	if (!cookie->fq_domain && (!dev || !dev_is_untrusted(dev)) &&
> 	    domain->ops->flush_iotlb_all && !iommu_get_dma_strict())
> 
> which is mixing up globals, device properties and domain properties. The
> result is that the driver code ends up just using the global to determine
> whether or not to pass IO_PGTABLE_QUIRK_NON_STRICT to the page-table code,
> which is a departure from the current way of doing things.

But previously, SMMU only ever saw the global policy piped through the 
domain attribute by iommu_group_alloc_default_domain(), so there's no 
functional change there.

Obviously some of the above checks could be factored out into some kind 
of iommu_use_flush_queue() helper that IOMMU drivers can also call if 
they need to keep in sync. Or maybe we just allow iommu-dma to set 
IO_PGTABLE_QUIRK_NON_STRICT directly via iommu_set_pgtable_quirks() if 
we're treating that as a generic thing now.

>>> For example, see the recent patch from Lu Baolu:
>>>
>>> https://lore.kernel.org/r/20210225061454.2864009-1-baolu.lu@linux.intel.com
>>
>> Erm, this patch is based on that one, it's right there in the context :/
> 
> Ah, sorry, I didn't spot that! I was just trying to illustrate that this
> is per-device.

Sure, I understand - and I'm just trying to bang home that despite 
appearances it's never actually been treated as such for SMMU, so 
anything that's wrong after this change was already wrong before.

Robin.

  reply	other threads:[~2021-03-30 16:29 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-16 15:38 cleanup unused or almost unused IOMMU APIs and the FSL PAMU driver v2 Christoph Hellwig
2021-03-16 15:38 ` [PATCH 01/18] iommu: remove the unused domain_window_disable method Christoph Hellwig
2021-03-30 12:04   ` Will Deacon
2021-03-16 15:38 ` [PATCH 02/18] iommu/fsl_pamu: remove fsl_pamu_get_domain_attr Christoph Hellwig
2021-03-30 12:10   ` Will Deacon
2021-03-16 15:38 ` [PATCH 03/18] iommu/fsl_pamu: remove support for setting DOMAIN_ATTR_GEOMETRY Christoph Hellwig
2021-03-30 12:15   ` Will Deacon
2021-03-16 15:38 ` [PATCH 04/18] iommu/fsl_pamu: merge iommu_alloc_dma_domain into fsl_pamu_domain_alloc Christoph Hellwig
2021-03-30 12:17   ` Will Deacon
2021-03-16 15:38 ` [PATCH 05/18] iommu/fsl_pamu: remove support for multiple windows Christoph Hellwig
2021-03-30 12:22   ` Will Deacon
2021-04-01  9:29     ` Christoph Hellwig
2021-03-16 15:38 ` [PATCH 06/18] iommu/fsl_pamu: remove ->domain_window_enable Christoph Hellwig
2021-03-30 12:40   ` Will Deacon
2021-04-01  9:32     ` Christoph Hellwig
2021-03-16 15:38 ` [PATCH 07/18] iommu/fsl_pamu: replace DOMAIN_ATTR_FSL_PAMU_STASH with a direct call Christoph Hellwig
2021-03-30 12:44   ` Will Deacon
2021-03-16 15:38 ` [PATCH 08/18] iommu/fsl_pamu: merge pamu_set_liodn and map_liodn Christoph Hellwig
2021-03-30 12:46   ` Will Deacon
2021-04-01  9:34     ` Christoph Hellwig
2021-03-16 15:38 ` [PATCH 09/18] iommu/fsl_pamu: merge handle_attach_device into fsl_pamu_attach_device Christoph Hellwig
2021-03-30 12:48   ` Will Deacon
2021-03-16 15:38 ` [PATCH 10/18] iommu/fsl_pamu: enable the liodn when attaching a device Christoph Hellwig
2021-03-30 12:53   ` Will Deacon
2021-03-16 15:38 ` [PATCH 11/18] iommu/fsl_pamu: remove the snoop_id field Christoph Hellwig
2021-03-30 12:58   ` Will Deacon
2021-04-01  9:36     ` Christoph Hellwig
2021-03-16 15:38 ` [PATCH 12/18] iommu: remove DOMAIN_ATTR_PAGING Christoph Hellwig
2021-03-30 12:58   ` Will Deacon
2021-03-16 15:38 ` [PATCH 13/18] iommu: remove DOMAIN_ATTR_GEOMETRY Christoph Hellwig
2021-03-30 13:00   ` Will Deacon
2021-03-16 15:38 ` [PATCH 14/18] iommu: remove DOMAIN_ATTR_NESTING Christoph Hellwig
2021-03-30 13:04   ` Will Deacon
2021-03-16 15:38 ` [PATCH 15/18] iommu: remove iommu_set_cmd_line_dma_api and iommu_cmd_line_dma_api Christoph Hellwig
2021-03-30 13:05   ` Will Deacon
2021-03-16 15:38 ` [PATCH 16/18] iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE Christoph Hellwig
2021-03-30 13:11   ` Will Deacon
2021-03-30 13:19     ` Robin Murphy
2021-03-30 13:58       ` Will Deacon
2021-03-30 16:28         ` Robin Murphy [this message]
2021-03-31 11:49           ` Will Deacon
2021-03-31 13:09             ` Robin Murphy
2021-03-31 15:32               ` Will Deacon
2021-03-31 16:05                 ` Robin Murphy
2021-04-01  9:59                   ` Christoph Hellwig
2021-04-01 13:26                     ` Will Deacon
2021-03-31 16:07   ` Robin Murphy
2021-03-16 15:38 ` [PATCH 17/18] iommu: remove DOMAIN_ATTR_IO_PGTABLE_CFG Christoph Hellwig
2021-03-30 13:14   ` Will Deacon
2021-03-16 15:38 ` [PATCH 18/18] iommu: remove iommu_domain_{get,set}_attr Christoph Hellwig
2021-03-30 13:16   ` Will Deacon

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