From: Fenghua Yu <fenghua.yu@intel.com>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>,
Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Vinod Koul <vkoul@kernel.org>, Dave Jiang <dave.jiang@intel.com>,
<dmaengine@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Alistair Popple <apopple@nvidia.com>,
Joerg Roedel <joro@8bytes.org>, "Will Deacon" <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
"Lorenzo Stoakes" <lstoakes@gmail.com>,
Christoph Hellwig <hch@infradead.org>, <iommu@lists.linux.dev>
Subject: Re: [PATCH v2 08/16] iommu: define and export iommu_access_remote_vm()
Date: Tue, 7 Mar 2023 08:33:07 -0800 [thread overview]
Message-ID: <156f9e28-e7d2-b443-1aa5-1f5447cb9bbd@intel.com> (raw)
In-Reply-To: <20230307084058.GA1330745@myrica>
Hi, Jean,
On 3/7/23 00:40, Jean-Philippe Brucker wrote:
> Hi Fenghua,
>
> On Mon, Mar 06, 2023 at 08:31:30AM -0800, Fenghua Yu wrote:
>> Define and export iommu_access_remote_vm() to allow IOMMU related
>> drivers to access user address space by PASID.
>>
>> The IDXD driver would like to use it to write the user's completion
>> record that the hardware device is not able to write to due to user
>> page fault.
>>
>> Without the API, it's complex for IDXD driver to copy completion record
>> to a process' fault address for two reasons:
>> 1. access_remote_vm() is not exported and shouldn't be exported for
>> drivers because drivers may easily cause mm reference issue.
>> 2. user frees fault address pages to trigger fault by IDXD device.
>>
>> The driver has to call iommu_sva_find(), kthread_use_mm(), re-implement
>> majority of access_remote_vm() etc to access remote vm.
>>
>> This IOMMU specific API hides these details and provides a clean interface
>> for idxd driver and potentially other IOMMU related drivers.
>>
>> Suggested-by: Alistair Popple <apopple@nvidia.com>
>> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
>> Cc: Joerg Roedel <joro@8bytes.org>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Robin Murphy <robin.murphy@arm.com>
>> Cc: Alistair Popple <apopple@nvidia.com>
>> Cc: Lorenzo Stoakes <lstoakes@gmail.com>
>> Cc: Christoph Hellwig <hch@infradead.org>
>> Cc: iommu@lists.linux.dev
>> ---
>> v2:
>> - Define and export iommu_access_remote_vm() for IDXD driver to write
>> completion record to user address space. This change removes
>> patch 8 and 9 in v1 (Alistair Popple)
>>
>> drivers/iommu/iommu-sva.c | 35 +++++++++++++++++++++++++++++++++++
>> include/linux/iommu.h | 9 +++++++++
>> 2 files changed, 44 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
>> index 24bf9b2b58aa..1d7a0aee58f7 100644
>> --- a/drivers/iommu/iommu-sva.c
>> +++ b/drivers/iommu/iommu-sva.c
>> @@ -71,6 +71,41 @@ struct mm_struct *iommu_sva_find(ioasid_t pasid)
>> }
>> EXPORT_SYMBOL_GPL(iommu_sva_find);
>>
>> +/**
>> + * iommu_access_remote_vm - access another process' address space by PASID
>> + * @pasid: Process Address Space ID assigned to the mm
>> + * @addr: start address to access
>> + * @buf: source or destination buffer
>> + * @len: number of bytes to transfer
>> + * @gup_flags: flags modifying lookup behaviour
>> + *
>> + * Another process' address space is found by PASID. A reference on @mm
>> + * is taken and released inside the function.
>> + *
>> + * Return: number of bytes copied from source to destination.
>> + */
>> +int iommu_access_remote_vm(ioasid_t pasid, unsigned long addr, void *buf,
>> + int len, unsigned int gup_flags)
>> +{
>> + struct mm_struct *mm;
>> + int copied;
>> +
>> + mm = iommu_sva_find(pasid);
>
> The ability to find a mm by PASID is being removed, see
> https://lore.kernel.org/linux-iommu/20230301235646.2692846-4-jacob.jun.pan@linux.intel.com/
>
Thank you very much for pointing out this.
I talked to Jacob just now. He will keep iommu_sva_find() function
in his next version because this patch is still using the function. He
agrees that I can still call iommu_sva_find() in this patch.
-Fenghua
next prev parent reply other threads:[~2023-03-07 16:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 16:31 [PATCH v2 00/16] Enable DSA 2.0 Event Log and completion record faulting features Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 01/16] dmaengine: idxd: make misc interrupt one shot Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 02/16] dmaengine: idxd: add event log size sysfs attribute Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 03/16] dmaengine: idxd: setup event log configuration Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 04/16] dmaengine: idxd: add interrupt handling for event log Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 05/16] dmanegine: idxd: add debugfs for event log dump Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 06/16] dmaengine: idxd: add per DSA wq workqueue for processing cr faults Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 07/16] dmaengine: idxd: create kmem cache for event log fault items Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 08/16] iommu: define and export iommu_access_remote_vm() Fenghua Yu
2023-03-07 1:41 ` Baolu Lu
2023-03-07 17:55 ` Fenghua Yu
2023-03-08 2:23 ` Baolu Lu
2023-03-20 13:35 ` Christoph Hellwig
2023-03-31 0:44 ` Fenghua Yu
2023-03-07 8:40 ` Jean-Philippe Brucker
2023-03-07 16:33 ` Fenghua Yu [this message]
2023-03-11 17:31 ` Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 09/16] dmaengine: idxd: process user page faults for completion record Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 10/16] dmaengine: idxd: add descs_completed field " Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 11/16] dmaengine: idxd: process batch descriptor completion record faults Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 12/16] dmaengine: idxd: add per file user counters for " Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 13/16] dmaengine: idxd: add a device to represent the file opened Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 14/16] dmaengine: idxd: expose fault counters to sysfs Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 15/16] dmaengine: idxd: add pid to exported sysfs attribute for opened file Fenghua Yu
2023-03-06 16:31 ` [PATCH v2 16/16] dmaengine: idxd: add per wq PRS disable Fenghua Yu
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