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Subject: Re: [PATCH v2 2/7] iommu/dma-iommu: Split iommu_dma_map_msi_msg() in
 two parts
To:     Julien Grall <julien.grall@arm.com>, linux-kernel@vger.kernel.org,
        iommu@lists.linux-foundation.org
Cc:     logang@deltatee.com, douliyangs@gmail.com,
        miquel.raynal@bootlin.com, marc.zyngier@arm.com,
        jason@lakedaemon.net, tglx@linutronix.de, joro@8bytes.org,
        bigeasy@linutronix.de, linux-rt-users@vger.kernel.org
References: <20190429144428.29254-1-julien.grall@arm.com>
 <20190429144428.29254-3-julien.grall@arm.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <ccd4d18a-63a4-893b-d2cf-771ad104329d@arm.com>
Date:   Mon, 29 Apr 2019 16:16:46 +0100
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On 29/04/2019 15:44, Julien Grall wrote:
> On RT, iommu_dma_map_msi_msg() may be called from non-preemptible
> context. This will lead to a splat with CONFIG_DEBUG_ATOMIC_SLEEP as
> the function is using spin_lock (they can sleep on RT).
> 
> iommu_dma_map_msi_msg() is used to map the MSI page in the IOMMU PT
> and update the MSI message with the IOVA.
> 
> Only the part to lookup for the MSI page requires to be called in
> preemptible context. As the MSI page cannot change over the lifecycle
> of the MSI interrupt, the lookup can be cached and re-used later on.
> 
> iomma_dma_map_msi_msg() is now split in two functions:
>      - iommu_dma_prepare_msi(): This function will prepare the mapping
>      in the IOMMU and store the cookie in the structure msi_desc. This
>      function should be called in preemptible context.
>      - iommu_dma_compose_msi_msg(): This function will update the MSI
>      message with the IOVA when the device is behind an IOMMU.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
> 
> ---
>      Changes in v2:
>          - Rework the commit message to use imperative mood
>          - Use the MSI accessor to get/set the iommu cookie
>          - Don't use ternary on return
>          - Select CONFIG_IRQ_MSI_IOMMU
>          - Pass an msi_desc rather than the irq number
> ---
>   drivers/iommu/Kconfig     |  1 +
>   drivers/iommu/dma-iommu.c | 47 ++++++++++++++++++++++++++++++++++++++---------
>   include/linux/dma-iommu.h | 23 +++++++++++++++++++++++
>   3 files changed, 62 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 6f07f3b21816..eb1c8cd243f9 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -94,6 +94,7 @@ config IOMMU_DMA
>   	bool
>   	select IOMMU_API
>   	select IOMMU_IOVA
> +	select IRQ_MSI_IOMMU
>   	select NEED_SG_DMA_LENGTH
>   
>   config FSL_PAMU
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 77aabe637a60..2309f59cefa4 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -888,17 +888,18 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
>   	return NULL;
>   }
>   
> -void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
> +int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
>   {
> -	struct device *dev = msi_desc_to_dev(irq_get_msi_desc(irq));
> +	struct device *dev = msi_desc_to_dev(desc);
>   	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
>   	struct iommu_dma_cookie *cookie;
>   	struct iommu_dma_msi_page *msi_page;
> -	phys_addr_t msi_addr = (u64)msg->address_hi << 32 | msg->address_lo;
>   	unsigned long flags;
>   
> -	if (!domain || !domain->iova_cookie)
> -		return;
> +	if (!domain || !domain->iova_cookie) {
> +		desc->iommu_cookie = NULL;
> +		return 0;
> +	}
>   
>   	cookie = domain->iova_cookie;
>   
> @@ -911,7 +912,37 @@ void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
>   	msi_page = iommu_dma_get_msi_page(dev, msi_addr, domain);
>   	spin_unlock_irqrestore(&cookie->msi_lock, flags);
>   
> -	if (WARN_ON(!msi_page)) {
> +	msi_desc_set_iommu_cookie(desc, msi_page);
> +
> +	if (!msi_page)
> +		return -ENOMEM;
> +	else

Nit: the "else" isn't really necessary.

> +		return 0;
> +}
> +
> +void iommu_dma_compose_msi_msg(struct msi_desc *desc,
> +			       struct msi_msg *msg)
> +{
> +	struct device *dev = msi_desc_to_dev(desc);
> +	const struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +	const struct iommu_dma_msi_page *msi_page;
> +
> +	msi_page = msi_desc_get_iommu_cookie(desc);
> +
> +	if (!domain || !domain->iova_cookie || WARN_ON(!msi_page))
> +		return;
> +
> +	msg->address_hi = upper_32_bits(msi_page->iova);
> +	msg->address_lo &= cookie_msi_granule(domain->iova_cookie) - 1;
> +	msg->address_lo += lower_32_bits(msi_page->iova);
> +}
> +
> +void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
> +{
> +	struct msi_desc *desc = irq_get_msi_desc(irq);
> +	phys_addr_t msi_addr = (u64)msg->address_hi << 32 | msg->address_lo;
> +
> +	if (WARN_ON(iommu_dma_prepare_msi(desc, msi_addr))) {
>   		/*
>   		 * We're called from a void callback, so the best we can do is
>   		 * 'fail' by filling the message with obviously bogus values.
> @@ -922,8 +953,6 @@ void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
>   		msg->address_lo = ~0U;
>   		msg->data = ~0U;
>   	} else {
> -		msg->address_hi = upper_32_bits(msi_page->iova);
> -		msg->address_lo &= cookie_msi_granule(cookie) - 1;
> -		msg->address_lo += lower_32_bits(msi_page->iova);
> +		iommu_dma_compose_msi_msg(desc, msg);
>   	}
>   }
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> index e760dc5d1fa8..3fc48fbd6f63 100644
> --- a/include/linux/dma-iommu.h
> +++ b/include/linux/dma-iommu.h
> @@ -71,12 +71,24 @@ void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
>   		size_t size, enum dma_data_direction dir, unsigned long attrs);
>   
>   /* The DMA API isn't _quite_ the whole story, though... */
> +/*
> + * Map the MSI page in the IOMMU device and store it in @desc
> + *
> + * Return 0 if succeeded other an error if the preparation has failed.
> + */

Nit: If you want to document these, please use proper kerneldoc comments 
on the definitions, rather than ad-hoc ones on the declarations.

Modulo that, though:

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> +int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr);
> +
> +/* Update the MSI message if required. */
> +void iommu_dma_compose_msi_msg(struct msi_desc *desc,
> +			       struct msi_msg *msg);
> +
>   void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg);
>   void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list);
>   
>   #else
>   
>   struct iommu_domain;
> +struct msi_desc;
>   struct msi_msg;
>   struct device;
>   
> @@ -99,6 +111,17 @@ static inline void iommu_put_dma_cookie(struct iommu_domain *domain)
>   {
>   }
>   
> +static inline int iommu_dma_prepare_msi(struct msi_desc *desc,
> +					phys_addr_t msi_addr)
> +{
> +	return 0;
> +}
> +
> +static inline void iommu_dma_compose_msi_msg(struct msi_desc *desc,
> +					     struct msi_msg *msg)
> +{
> +}
> +
>   static inline void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
>   {
>   }
>