From: Lu Baolu <baolu.lu@linux.intel.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: kevin.tian@intel.com, ashok.raj@intel.com,
sanjay.k.kumar@intel.com, linux-kernel@vger.kernel.org,
iommu@lists.linux-foundation.org, jacob.jun.pan@intel.com,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH 2/5] iommu/vt-d: Remove WO permissions on second-level paging entries
Date: Mon, 8 Mar 2021 09:58:26 +0800 [thread overview]
Message-ID: <c7bffaee-6c3c-3254-a71a-d66d023d1e58@linux.intel.com> (raw)
In-Reply-To: <20210304122623.GD26414@8bytes.org>
Hi Joerg,
On 3/4/21 8:26 PM, Joerg Roedel wrote:
> On Thu, Feb 25, 2021 at 02:26:51PM +0800, Lu Baolu wrote:
>> When the first level page table is used for IOVA translation, it only
>> supports Read-Only and Read-Write permissions. The Write-Only permission
>> is not supported as the PRESENT bit (implying Read permission) should
>> always set. When using second level, we still give separate permissions
>> that allows WriteOnly which seems inconsistent and awkward. There is no
>> use case we can think off, hence remove that configuration to make it
>> consistent.
>
> No use-case for WriteOnly mappings? How about DMA_FROM_DEVICE mappings?
>
The statement of no use case is not correct. Sorry about it.
As we have moved to use first level for IOVA translation, the first
level page table entry only provides RO and RW permissions. So if any
device driver specifies DMA_FROM_DEVICE attribution, it will get RW
permission in the page table. This patch aims to make the permissions
of second level and first level consistent. No impact on the use of
DMA_FROM_DEVICE attribution.
Best regards,
baolu
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next prev parent reply other threads:[~2021-03-08 2:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 6:26 [PATCH 0/5] iommu/vt-d: Several misc fixes Lu Baolu
2021-02-25 6:26 ` [PATCH 1/5] iommu/vt-d: Report the right page fault address Lu Baolu
2021-02-25 6:26 ` [PATCH 2/5] iommu/vt-d: Remove WO permissions on second-level paging entries Lu Baolu
2021-03-04 12:26 ` Joerg Roedel
2021-03-08 1:58 ` Lu Baolu [this message]
2021-03-08 19:47 ` Raj, Ashok
2021-03-18 9:12 ` Joerg Roedel
2021-03-19 0:24 ` Lu Baolu
2021-02-25 6:26 ` [PATCH 3/5] iommu/vt-d: Invalidate PASID cache when root/context entry changed Lu Baolu
2021-02-25 6:26 ` [PATCH 4/5] iommu/vt-d: Use user privilege for RID2PASID translation Lu Baolu
2021-02-25 6:26 ` [PATCH 5/5] iommu/vt-d: Avoid unnecessary cache flush in pasid entry teardown Lu Baolu
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