Message-ID: <f4247831-5dbe-20f1-cd09-ef076137dc38@redhat.com>
Date:   Mon, 18 Jan 2021 16:41:40 +0800
From:   lijiang <lijiang@...hat.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     linux-kernel@...r.kernel.org,
        "Lendacky, Thomas" <thomas.lendacky@....com>, jroedel@...e.de,
        iommu@...ts.linux-foundation.org, will@...nel.org
Subject: Re: [PATCH] iommu: check for the deferred attach when attaching a
 device

在 2021年01月15日 23:15, Robin Murphy 写道:
> On 2021-01-15 14:26, lijiang wrote:
>> Hi, Robin
>>
>> Thank you for the comment.
>>
>> 在 2021年01月13日 01:29, Robin Murphy 写道:
>>> On 2021-01-05 07:52, lijiang wrote:
>>>> 在 2021年01月05日 11:55, lijiang 写道:
>>>>> Hi,
>>>>>
>>>>> Also add Joerg to cc list.
>>>>>
>>>>
>>>> Also add more people to cc list, Jerry Snitselaar and Tom Lendacky.
>>>>
>>>> Thanks.
>>>>
>>>>> Thanks.
>>>>> Lianbo
>>>>> 在 2020年12月26日 13:39, Lianbo Jiang 写道:
>>>>>> Currently, because domain attach allows to be deferred from iommu
>>>>>> driver to device driver, and when iommu initializes, the devices
>>>>>> on the bus will be scanned and the default groups will be allocated.
>>>>>>
>>>>>> Due to the above changes, some devices could be added to the same
>>>>>> group as below:
>>>>>>
>>>>>> [    3.859417] pci 0000:01:00.0: Adding to iommu group 16
>>>>>> [    3.864572] pci 0000:01:00.1: Adding to iommu group 16
>>>>>> [    3.869738] pci 0000:02:00.0: Adding to iommu group 17
>>>>>> [    3.874892] pci 0000:02:00.1: Adding to iommu group 17
>>>>>>
>>>>>> But when attaching these devices, it doesn't allow that a group has
>>>>>> more than one device, otherwise it will return an error. This conflicts
>>>>>> with the deferred attaching. Unfortunately, it has two devices in the
>>>>>> same group for my side, for example:
>>>>>>
>>>>>> [    9.627014] iommu_group_device_count(): device name[0]:0000:01:00.0
>>>>>> [    9.633545] iommu_group_device_count(): device name[1]:0000:01:00.1
>>>>>> ...
>>>>>> [   10.255609] iommu_group_device_count(): device name[0]:0000:02:00.0
>>>>>> [   10.262144] iommu_group_device_count(): device name[1]:0000:02:00.1
>>>>>>
>>>>>> Finally, which caused the failure of tg3 driver when tg3 driver calls
>>>>>> the dma_alloc_coherent() to allocate coherent memory in the tg3_test_dma().
>>>>>>
>>>>>> [    9.660310] tg3 0000:01:00.0: DMA engine test failed, aborting
>>>>>> [    9.754085] tg3: probe of 0000:01:00.0 failed with error -12
>>>>>> [    9.997512] tg3 0000:01:00.1: DMA engine test failed, aborting
>>>>>> [   10.043053] tg3: probe of 0000:01:00.1 failed with error -12
>>>>>> [   10.288905] tg3 0000:02:00.0: DMA engine test failed, aborting
>>>>>> [   10.334070] tg3: probe of 0000:02:00.0 failed with error -12
>>>>>> [   10.578303] tg3 0000:02:00.1: DMA engine test failed, aborting
>>>>>> [   10.622629] tg3: probe of 0000:02:00.1 failed with error -12
>>>>>>
>>>>>> In addition, the similar situations also occur in other drivers such
>>>>>> as the bnxt_en driver. That can be reproduced easily in kdump kernel
>>>>>> when SME is active.
>>>>>>
>>>>>> Add a check for the deferred attach in the iommu_attach_device() and
>>>>>> allow to attach the deferred device regardless of how many devices
>>>>>> are in a group.
>>>
>>> Is this iommu_attach_device() call is coming from iommu-dma? (if not, then whoever's calling it probably shouldn't be)
>>>
>>
>> Yes, you are right, the iommu_attach_device call is coming from iommu-dma.
>>  
>>> Assuming so, then probably what should happen is to move the handling currently in iommu_dma_deferred_attach() into the core so that it can call __iommu_attach_device() directly - the intent is just to replay that exact call skipped in iommu_group_add_device(), so the legacy external iommu_attach_device() interface isn't really the right tool for the job
>>
>> Sounds good. I will check if this can work in various cases. If it's OK, I will post again.
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index f0305e6aac1b..5e7da902ac36 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -23,7 +23,6 @@
>>   #include <linux/swiotlb.h>
>>   #include <linux/scatterlist.h>
>>   #include <linux/vmalloc.h>
>> -#include <linux/crash_dump.h>
>>   #include <linux/dma-direct.h>
>>     struct iommu_dma_msi_page {
>> @@ -378,21 +377,6 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>>       return iova_reserve_iommu_regions(dev, domain);
>>   }
>>   -static int iommu_dma_deferred_attach(struct device *dev,
>> -        struct iommu_domain *domain)
>> -{
>> -    const struct iommu_ops *ops = domain->ops;
>> -
>> -    if (!is_kdump_kernel())
>> -        return 0;
>> -
>> -    if (unlikely(ops->is_attach_deferred &&
>> -            ops->is_attach_deferred(domain, dev)))
>> -        return iommu_attach_device(domain, dev);
>> -
>> -    return 0;
>> -}
>> -
>>   /**
>>    * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
>>    *                    page flags.
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index ffeebda8d6de..4fed1567b498 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -23,6 +23,7 @@
>>   #include <linux/property.h>
>>   #include <linux/fsl/mc.h>
>>   #include <linux/module.h>
>> +#include <linux/crash_dump.h>
>>   #include <trace/events/iommu.h>
>>     static struct kset *iommu_group_kset;
>> @@ -1952,6 +1953,21 @@ static int __iommu_attach_device(struct iommu_domain *domain,
>>       return ret;
>>   }
>>   +int iommu_dma_deferred_attach(struct device *dev,
>> +                struct iommu_domain *domain)
>> +{
>> +        const struct iommu_ops *ops = domain->ops;
>> +
>> +        if (!is_kdump_kernel())
>> +                return 0;
>> +
>> +        if (unlikely(ops->is_attach_deferred &&
>> +                        ops->is_attach_deferred(domain, dev)))
>> +                return __iommu_attach_device(domain, dev);
>> +
>> +        return 0;
>> +}
>> +
>>   int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>>   {
>>       struct iommu_group *group;
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index b3f0e2018c62..8e0ee96ca456 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -424,6 +424,8 @@ extern struct iommu_group *iommu_group_get_by_id(int id);
>>   extern void iommu_domain_free(struct iommu_domain *domain);
>>   extern int iommu_attach_device(struct iommu_domain *domain,
>>                      struct device *dev);
>> +extern int iommu_dma_deferred_attach(struct device *dev,
>> +                struct iommu_domain *domain);
>>   extern void iommu_detach_device(struct iommu_domain *domain,
>>                   struct device *dev);
>>   extern int iommu_uapi_cache_invalidate(struct iommu_domain *domain,
>> @@ -680,6 +682,12 @@ static inline int iommu_attach_device(struct iommu_domain *domain,
>>       return -ENODEV;
>>   }
>>   +static inline int iommu_dma_deferred_attach(struct device *dev,
>> +                        struct iommu_domain *domain)
>> +{
>> +    return -ENODEV;
>> +}
>> +
>>   static inline void iommu_detach_device(struct iommu_domain *domain,
>>                          struct device *dev)
>>   {
> 
> Yeah, that's more or less what I had in mind (FWIW I don't think we need the stub definition since this should only ever be called by other IOMMU-API-dependent code).

Seems yes, I can remove the stub definition. I just checked the driver/iommu/Kconfig, the IOMMU_API always gets selected by default, and the IOMMU_DMA depends on IOMMU_API.

> However I'd really like to minimise the fast-path impact to the normal case, so how about throwing something like this into the mix as well? 

That's good idea although the implementation of the is_kdump_kernel() is very simple. But I could split them into two patches so that it can be
reviewed conveniently:

[1] [PATCH 1/2] dma-iommu: use static-key to minimize the impact in the fast-path

Let's move out the is_kdump_kernel() check from iommu_dma_deferred_attach()
to iommu_dma_init(), and use the static-key in the fast-path to minimize the
impact in the normal case.

[2] [PATCH 2/2] iommu: use the __iommu_attach_device() directly for 
 deffered attach

Let's move the handling currently in iommu_dma_deferred_attach() into
the iommu core code so that it can call the __iommu_attach_device()
directly instead of the iommu_attach_device(). And change the name of
iommu_dma_deferred_attach() to iommu_do_deferred_attach().


>(where iommu_do_deferred_attach() represents what you have above minus the move of the kdump check)
>
OK, understood, thanks. Would you mind adding your Signed-off-by to these patches when I post again? If you
have no objection, I will post these two changes(patches) later.


Thanks.
Lianbo
 
> Cheers,
> Robin.
> 
> ----->8-----
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 4078358ed66e..638222558248 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -51,6 +51,8 @@ struct iommu_dma_cookie {
>      struct iommu_domain        *fq_domain;
>  };
> 
> +DEFINE_STATIC_KEY_FALSE(deferred_attach);
> +
>  void iommu_dma_free_cpu_cached_iovas(unsigned int cpu,
>          struct iommu_domain *domain)
>  {
> @@ -378,21 +380,6 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
>      return iova_reserve_iommu_regions(dev, domain);
>  }
> 
> -static int iommu_dma_deferred_attach(struct device *dev,
> -        struct iommu_domain *domain)
> -{
> -    const struct iommu_ops *ops = domain->ops;
> -
> -    if (!is_kdump_kernel())
> -        return 0;
> -
> -    if (unlikely(ops->is_attach_deferred &&
> -            ops->is_attach_deferred(domain, dev)))
> -        return iommu_attach_device(domain, dev);
> -
> -    return 0;
> -}
> -
>  /**
>   * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
>   *                    page flags.
> @@ -535,7 +522,8 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
>      size_t iova_off = iova_offset(iovad, phys);
>      dma_addr_t iova;
> 
> -    if (unlikely(iommu_dma_deferred_attach(dev, domain)))
> +    if (static_branch_unlikely(&deferred_attach) &&
> +        iommu_do_deferred_attach(domain, dev))
>          return DMA_MAPPING_ERROR;
> 
>      size = iova_align(iovad, size + iova_off);
> @@ -693,7 +681,8 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
> 
>      *dma_handle = DMA_MAPPING_ERROR;
> 
> -    if (unlikely(iommu_dma_deferred_attach(dev, domain)))
> +    if (static_branch_unlikely(&deferred_attach) &&
> +        iommu_do_deferred_attach(domain, dev))
>          return NULL;
> 
>      min_size = alloc_sizes & -alloc_sizes;
> @@ -976,7 +965,8 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
>      unsigned long mask = dma_get_seg_boundary(dev);
>      int i;
> 
> -    if (unlikely(iommu_dma_deferred_attach(dev, domain)))
> +    if (static_branch_unlikely(&deferred_attach) &&
> +        iommu_do_deferred_attach(domain, dev))
>          return 0;
> 
>      if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> @@ -1424,6 +1414,9 @@ void iommu_dma_compose_msi_msg(struct msi_desc *desc,
> 
>  static int iommu_dma_init(void)
>  {
> +    if (is_kdump_kernel())
> +        static_branch_enable(&deferred_attach);
> +
>      return iova_cache_get();
>  }
>  arch_initcall(iommu_dma_init);
> 

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