From: Lu Baolu <baolu.lu@linux.intel.com>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
vivek.gautam@arm.com, guohanjun@huawei.com, will@kernel.org,
lorenzo.pieralisi@arm.com, joro@8bytes.org,
Zhou Wang <wangzhou1@hisilicon.com>,
linux-acpi@vger.kernel.org, zhangfei.gao@linaro.org,
lenb@kernel.org, devicetree@vger.kernel.org, "Tian,
Kevin" <kevin.tian@intel.com>, Arnd Bergmann <arnd@arndb.de>,
eric.auger@redhat.com, robh+dt@kernel.org,
Jonathan.Cameron@huawei.com,
linux-arm-kernel@lists.infradead.org,
David Woodhouse <dwmw2@infradead.org>,
rjw@rjwysocki.net, shameerali.kolothum.thodi@huawei.com,
iommu@lists.linux-foundation.org, sudeep.holla@arm.com,
robin.murphy@arm.com, linux-accelerators@lists.ozlabs.org,
baolu.lu@linux.intel.com
Subject: Re: [PATCH v9 03/10] iommu: Separate IOMMU_DEV_FEAT_IOPF from IOMMU_DEV_FEAT_SVA
Date: Wed, 13 Jan 2021 10:49:39 +0800 [thread overview]
Message-ID: <c88e5d74-098d-7f1d-a7bb-a89e40fb8fa4@linux.intel.com> (raw)
In-Reply-To: <X/1o72DTmzdCMhDz@myrica>
Hi Jean,
On 1/12/21 5:16 PM, Jean-Philippe Brucker wrote:
> Hi Baolu,
>
> On Tue, Jan 12, 2021 at 12:31:23PM +0800, Lu Baolu wrote:
>> Hi Jean,
>>
>> On 1/8/21 10:52 PM, Jean-Philippe Brucker wrote:
>>> Some devices manage I/O Page Faults (IOPF) themselves instead of relying
>>> on PCIe PRI or Arm SMMU stall. Allow their drivers to enable SVA without
>>> mandating IOMMU-managed IOPF. The other device drivers now need to first
>>> enable IOMMU_DEV_FEAT_IOPF before enabling IOMMU_DEV_FEAT_SVA.
>>>
>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
>>> ---
>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>> Cc: David Woodhouse <dwmw2@infradead.org>
>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> Cc: Joerg Roedel <joro@8bytes.org>
>>> Cc: Lu Baolu <baolu.lu@linux.intel.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
>>> Cc: Zhou Wang <wangzhou1@hisilicon.com>
>>> ---
>>> include/linux/iommu.h | 20 +++++++++++++++++---
>>> 1 file changed, 17 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>>> index 583c734b2e87..701b2eeb0dc5 100644
>>> --- a/include/linux/iommu.h
>>> +++ b/include/linux/iommu.h
>>> @@ -156,10 +156,24 @@ struct iommu_resv_region {
>>> enum iommu_resv_type type;
>>> };
>>> -/* Per device IOMMU features */
>>> +/**
>>> + * enum iommu_dev_features - Per device IOMMU features
>>> + * @IOMMU_DEV_FEAT_AUX: Auxiliary domain feature
>>> + * @IOMMU_DEV_FEAT_SVA: Shared Virtual Addresses
>>> + * @IOMMU_DEV_FEAT_IOPF: I/O Page Faults such as PRI or Stall. Generally using
>>> + * %IOMMU_DEV_FEAT_SVA requires %IOMMU_DEV_FEAT_IOPF, but
>>> + * some devices manage I/O Page Faults themselves instead
>>> + * of relying on the IOMMU. When supported, this feature
>>> + * must be enabled before and disabled after
>>> + * %IOMMU_DEV_FEAT_SVA.
>>
>> Is this only for SVA? We may see more scenarios of using IOPF. For
>> example, when passing through devices to user level, the user's pages
>> could be managed dynamically instead of being allocated and pinned
>> statically.
>
> Hm, isn't that precisely what SVA does? I don't understand the
> difference. That said FEAT_IOPF doesn't have to be only for SVA. It could
> later be used as a prerequisite some another feature. For special cases
> device drivers can always use the iommu_register_device_fault_handler()
> API and handle faults themselves.
From the perspective of IOMMU, there is a little difference between
these two. For SVA, the page table is from CPU side, so IOMMU only needs
to call handle_mm_fault(); For above pass-through case, the page table
is from IOMMU side, so the device driver (probably VFIO) needs to
register a fault handler and call iommu_map/unmap() to serve the page
faults.
If we think about the nested mode (or dual-stage translation), it's more
complicated since the kernel (probably VFIO) handles the second level
page faults, while the first level page faults need to be delivered to
user-level guest. Obviously, this hasn't been fully implemented in any
IOMMU driver.
>
>> If @IOMMU_DEV_FEAT_IOPF is defined as generic iopf support, the current
>> vendor IOMMU driver support may not enough.
>
> IOMMU_DEV_FEAT_IOPF on its own doesn't do anything useful, it's mainly a
> way for device drivers to probe the IOMMU capability. Granted in patch
> 10 the SMMU driver registers the IOPF queue on enable() but that could be
> done by FEAT_SVA enable() instead, if we ever repurpose FEAT_IOPF.
I have no objection to split IOPF from SVA. Actually we must have this
eventually. My concern is that at this stage, the IOMMU drivers only
support SVA type of IOPF, a generic IOMMU_DEV_FEAT_IOPF feature might
confuse the device drivers which want to add other types of IOPF usage.
>
> Thanks,
> Jean
>
Best regards,
baolu
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next prev parent reply other threads:[~2021-01-13 2:59 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 14:52 [PATCH v9 00/10] iommu: I/O page faults for SMMUv3 Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 01/10] iommu: Remove obsolete comment Jean-Philippe Brucker
2021-01-19 11:11 ` Jonathan Cameron
2021-01-20 17:41 ` Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 02/10] iommu/arm-smmu-v3: Use device properties for pasid-num-bits Jean-Philippe Brucker
2021-01-19 11:22 ` Jonathan Cameron
2021-01-08 14:52 ` [PATCH v9 03/10] iommu: Separate IOMMU_DEV_FEAT_IOPF from IOMMU_DEV_FEAT_SVA Jean-Philippe Brucker
2021-01-12 4:31 ` Lu Baolu
2021-01-12 9:16 ` Jean-Philippe Brucker
2021-01-13 2:49 ` Lu Baolu [this message]
2021-01-13 8:10 ` Tian, Kevin
2021-01-14 16:41 ` Jean-Philippe Brucker
2021-01-16 3:54 ` Lu Baolu
2021-01-18 6:54 ` Tian, Kevin
2021-01-19 10:16 ` Jean-Philippe Brucker
2021-01-20 1:57 ` Lu Baolu
2021-01-08 14:52 ` [PATCH v9 04/10] iommu/vt-d: Support IOMMU_DEV_FEAT_IOPF Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 05/10] uacce: Enable IOMMU_DEV_FEAT_IOPF Jean-Philippe Brucker
2021-01-11 3:29 ` Zhangfei Gao
2021-01-19 12:27 ` Jonathan Cameron
2021-01-20 17:42 ` Jean-Philippe Brucker
2021-01-20 20:47 ` Dave Jiang
2021-01-22 11:53 ` Zhou Wang
2021-01-22 15:43 ` Dave Jiang
2021-01-08 14:52 ` [PATCH v9 06/10] iommu: Add a page fault handler Jean-Philippe Brucker
2021-01-19 13:38 ` Jonathan Cameron
2021-01-20 17:43 ` Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 07/10] iommu/arm-smmu-v3: Maintain a SID->device structure Jean-Philippe Brucker
2021-01-19 13:51 ` Jonathan Cameron
2021-01-08 14:52 ` [PATCH v9 08/10] dt-bindings: document stall property for IOMMU masters Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 09/10] ACPI/IORT: Enable stall support for platform devices Jean-Philippe Brucker
2021-01-08 14:52 ` [PATCH v9 10/10] iommu/arm-smmu-v3: Add " Jean-Philippe Brucker
2021-01-19 17:28 ` Robin Murphy
2021-01-20 17:55 ` Jean-Philippe Brucker
2021-01-11 3:26 ` [PATCH v9 00/10] iommu: I/O page faults for SMMUv3 Zhangfei Gao
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