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From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
To: will.deacon@arm.com
Cc: lorenzo.pieralisi@arm.com, zhongmiao@hisilicon.com,
	okaya@kernel.org, joro@8bytes.org, rjw@rjwysocki.net,
	linux-acpi@vger.kernel.org, iommu@lists.linux-foundation.org,
	hanjun.guo@linaro.org, sudeep.holla@arm.com,
	robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org,
	lenb@kernel.org
Subject: [PATCH 4/4] iommu/arm-smmu-v3: Disable tagged pointers
Date: Wed, 20 Mar 2019 17:36:34 +0000	[thread overview]
Message-ID: <20190320173634.21895-5-jean-philippe.brucker@arm.com> (raw)
In-Reply-To: <20190320173634.21895-1-jean-philippe.brucker@arm.com>

The ARM architecture has a "Top Byte Ignore" (TBI) option that makes the
MMU mask out bits [63:56] of an address, allowing a userspace application
to store data in its pointers. This option is incompatible with PCI ATS.

If TBI is enabled in the SMMU and userspace triggers DMA transactions on
tagged pointers, the endpoint might create ATC entries for addresses that
include a tag. Software would then have to send ATC invalidation packets
for each 255 possible alias of an address, or just wipe the whole address
space. This is not a viable option, so disable TBI.

The impact of this change is unclear, since there are very few users of
tagged pointers, much less SVA. But the requirement introduced by this
patch doesn't seem excessive: a userspace application using both tagged
pointers and SVA should now sanitize addresses (clear the tag) before
using them for device DMA.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index c605d6f1b2df..69afffdaf907 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1076,7 +1076,6 @@ static u64 arm_smmu_cpu_tcr_to_cd(u64 tcr)
 	val |= ARM_SMMU_TCR2CD(tcr, EPD0);
 	val |= ARM_SMMU_TCR2CD(tcr, EPD1);
 	val |= ARM_SMMU_TCR2CD(tcr, IPS);
-	val |= ARM_SMMU_TCR2CD(tcr, TBI0);
 
 	return val;
 }
-- 
2.21.0

WARNING: multiple messages have this Message-ID (diff)
From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
To: will.deacon@arm.com
Cc: lorenzo.pieralisi@arm.com, zhongmiao@hisilicon.com,
	okaya@kernel.org, joro@8bytes.org, rjw@rjwysocki.net,
	linux-acpi@vger.kernel.org, iommu@lists.linux-foundation.org,
	hanjun.guo@linaro.org, sudeep.holla@arm.com,
	robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org,
	lenb@kernel.org
Subject: [PATCH 4/4] iommu/arm-smmu-v3: Disable tagged pointers
Date: Wed, 20 Mar 2019 17:36:34 +0000	[thread overview]
Message-ID: <20190320173634.21895-5-jean-philippe.brucker@arm.com> (raw)
In-Reply-To: <20190320173634.21895-1-jean-philippe.brucker@arm.com>

The ARM architecture has a "Top Byte Ignore" (TBI) option that makes the
MMU mask out bits [63:56] of an address, allowing a userspace application
to store data in its pointers. This option is incompatible with PCI ATS.

If TBI is enabled in the SMMU and userspace triggers DMA transactions on
tagged pointers, the endpoint might create ATC entries for addresses that
include a tag. Software would then have to send ATC invalidation packets
for each 255 possible alias of an address, or just wipe the whole address
space. This is not a viable option, so disable TBI.

The impact of this change is unclear, since there are very few users of
tagged pointers, much less SVA. But the requirement introduced by this
patch doesn't seem excessive: a userspace application using both tagged
pointers and SVA should now sanitize addresses (clear the tag) before
using them for device DMA.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index c605d6f1b2df..69afffdaf907 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1076,7 +1076,6 @@ static u64 arm_smmu_cpu_tcr_to_cd(u64 tcr)
 	val |= ARM_SMMU_TCR2CD(tcr, EPD0);
 	val |= ARM_SMMU_TCR2CD(tcr, EPD1);
 	val |= ARM_SMMU_TCR2CD(tcr, IPS);
-	val |= ARM_SMMU_TCR2CD(tcr, TBI0);
 
 	return val;
 }
-- 
2.21.0


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2019-03-20 17:36 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-20 17:36 [PATCH 0/4] Add PCI ATS support to Arm SMMUv3 Jean-Philippe Brucker
2019-03-20 17:36 ` Jean-Philippe Brucker
2019-03-20 17:36 ` [PATCH 1/4] ACPI/IORT: Check ATS capability in root complex nodes Jean-Philippe Brucker
2019-03-20 17:36   ` Jean-Philippe Brucker
     [not found]   ` <20190320173634.21895-2-jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>
2019-03-21 16:00     ` Sinan Kaya
2019-03-21 16:00       ` Sinan Kaya
     [not found]       ` <fc53b2f7-53c4-c32d-8588-6f8d98ef5e7f-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2019-03-25 15:02         ` Jean-Philippe Brucker
2019-03-25 15:02           ` Jean-Philippe Brucker
2019-03-20 17:36 ` [PATCH 2/4] iommu/arm-smmu-v3: Link domains and devices Jean-Philippe Brucker
2019-03-20 17:36   ` Jean-Philippe Brucker
     [not found]   ` <20190320173634.21895-3-jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>
2019-04-04 14:39     ` Will Deacon
2019-04-04 14:39       ` Will Deacon
2019-04-05 16:35       ` Jean-Philippe Brucker
2019-04-05 16:35         ` Jean-Philippe Brucker
2019-04-05 16:35         ` Jean-Philippe Brucker
2019-04-05 16:35         ` Jean-Philippe Brucker
2019-04-05 16:39         ` Will Deacon
2019-04-05 16:39           ` Will Deacon
2019-04-05 16:39           ` Will Deacon
2019-04-05 16:39           ` Will Deacon
2019-04-05 18:07           ` Jean-Philippe Brucker
2019-04-05 18:07             ` Jean-Philippe Brucker
2019-04-05 18:07             ` Jean-Philippe Brucker
2019-04-05 18:07             ` Jean-Philippe Brucker
2019-03-20 17:36 ` [PATCH 3/4] iommu/arm-smmu-v3: Add support for PCI ATS Jean-Philippe Brucker
2019-03-20 17:36   ` Jean-Philippe Brucker
     [not found]   ` <20190320173634.21895-4-jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>
2019-03-21 15:52     ` Sinan Kaya
2019-03-21 15:52       ` Sinan Kaya
     [not found]       ` <6a4fb991-b8cd-d64d-25bd-dbbefcf69fa5-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2019-03-25 15:01         ` Jean-Philippe Brucker
2019-03-25 15:01           ` Jean-Philippe Brucker
2019-03-20 17:36 ` Jean-Philippe Brucker [this message]
2019-03-20 17:36   ` [PATCH 4/4] iommu/arm-smmu-v3: Disable tagged pointers Jean-Philippe Brucker

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