Re: [PATCH v7 2/6] iommu/dma: Add support for non-strict mode

From: Robin Murphy
Date: Tue Sep 18 2018 - 14:52:14 EST

On 2018-09-18 6:10 PM, Will Deacon wrote:
Hi Robin,

On Fri, Sep 14, 2018 at 03:30:20PM +0100, Robin Murphy wrote:
From: Zhen Lei <thunder.leizhen@xxxxxxxxxx>

1. Save the related domain pointer in struct iommu_dma_cookie, make iovad
capable call domain->ops->flush_iotlb_all to flush TLB.
2. During the iommu domain initialization phase, base on domain->non_strict
field to check whether non-strict mode is supported or not. If so, call
init_iova_flush_queue to register iovad->flush_cb callback.
3. All unmap(contains iova-free) APIs will finally invoke __iommu_dma_unmap
-->iommu_dma_free_iova. If the domain is non-strict, call queue_iova to
put off iova freeing, and omit iommu_tlb_sync operation.

Hmm, this is basically just a commentary on the code. Please could you write
it more in terms of the problem that's being solved?

Sure - I intentionally kept a light touch when it came to the documentation and commit messages in this rework (other than patch #1 where I eventually remembered the original reasoning and that it wasn't a bug). If we're more-or-less happy with the shape of the technical side I'll make sure to take a final pass through v8 to tidy up all the prose.

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
[rm: convert raw boolean to domain attribute]
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
drivers/iommu/dma-iommu.c | 29 ++++++++++++++++++++++++++++-
include/linux/iommu.h | 1 +
2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 511ff9a1d6d9..092e6926dc3c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -55,6 +55,9 @@ struct iommu_dma_cookie {
struct list_head msi_page_list;
spinlock_t msi_lock;
+ /* Only be assigned in non-strict mode, otherwise it's NULL */
+ struct iommu_domain *domain;
static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
@@ -257,6 +260,17 @@ static int iova_reserve_iommu_regions(struct device *dev,
return ret;
+static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
+ struct iommu_dma_cookie *cookie;
+ struct iommu_domain *domain;
+ cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
+ domain = cookie->domain;
+ domain->ops->flush_iotlb_all(domain);

Can we rely on this function pointer being non-NULL? I think it would
be better to call iommu_flush_tlb_all(cookie->domain) instead.

Yeah, that's deliberate - in fact got as far as writing that change, then undid it as I realised that although the attribute conversion got rid of the explicit ops->flush_iotlb_all check, it still makes zero sense for an IOMMU driver to claim to support the flush queue attribute without also providing the relevant callback, so I do actually want this to blow up rather than silently do nothing if that assumption isn't met.

* iommu_dma_init_domain - Initialise a DMA mapping domain
* @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
@@ -275,6 +289,7 @@ int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
struct iommu_dma_cookie *cookie = domain->iova_cookie;
struct iova_domain *iovad = &cookie->iovad;
unsigned long order, base_pfn, end_pfn;
+ int attr = 1;

Do we actually need to initialise this?

Oops, no, that's a left-over from the turned-out-messier-that-I-thought v6 implementation.