Re: [PATCH 2/7] iommu/dma-iommu: Split iommu_dma_map_msi_msg in two parts

[Julien Grall]

Hi Marc,

On 23/04/2019 11:54, Marc Zyngier wrote:
> On 18/04/2019 18:26, Julien Grall wrote:
> > On RT, the function 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).
> >
> > The function 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.
> >
> > This patch split the function iommu_dma_map_msi_msg in two new
> > 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@xxxxxxx>
> > ---
> >   drivers/iommu/dma-iommu.c | 43 ++++++++++++++++++++++++++++++++-----------
> >   include/linux/dma-iommu.h | 21 +++++++++++++++++++++
> >   2 files changed, 53 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index 77aabe637a60..f5c1f1685095 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -888,17 +888,17 @@ 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)
>
> I quite like the idea of moving from having an irq to having an msi_desc
> passed to the IOMMU layer...
>
> >   {
> > -	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;
> >   
> > @@ -908,10 +908,33 @@ void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
> >   	 * of an MSI from within an IPI handler.
> >   	 */
> >   	spin_lock_irqsave(&cookie->msi_lock, flags);
> > -	msi_page = iommu_dma_get_msi_page(dev, msi_addr, domain);
> > +	desc->iommu_cookie = iommu_dma_get_msi_page(dev, msi_addr, domain);
> >   	spin_unlock_irqrestore(&cookie->msi_lock, flags);
> >   
> > -	if (WARN_ON(!msi_page)) {
> > +	return (desc->iommu_cookie) ? 0 : -ENOMEM;
> > +}
> > +
> > +void iommu_dma_compose_msi_msg(int irq, struct msi_msg *msg)
>
> ... but I'd like it even better if it was uniform. Can you please move
> the irq_get_msi_desc() to the callers of iommu_dma_compose_msi_msg(),
> and make both functions take a msi_desc?

Make sense. I will modify iommu_dma_compose_msi_msg to take a msi_desc in parameter.

Cheers,

--
Julien Grall