iommu: Sort out domain user data

When DMA/MSI cookies were made first-class citizens back in commit
46983fcd67ac ("iommu: Pull IOVA cookie management into the core"), there
was no real need to further expose the two different cookie types.
However, now that IOMMUFD wants to add a third type of MSI-mapping
cookie, we do have a nicely compelling reason to properly dismabiguate
things at the domain level beyond just vaguely guessing from the domain
type.

Meanwhile, we also effectively have another "cookie" in the form of the
anonymous union for other user data, which isn't much better in terms of
being vague and unenforced. The fact is that all these cookie types are
mutually exclusive, in the sense that combining them makes zero sense
and/or would be catastrophic (iommu_set_fault_handler() on an SVA
domain, anyone?) - the only combination which *might* be reasonable is
perhaps a fault handler and an MSI cookie, but nobody's doing that at
the moment, so let's rule it out as well for the sake of being clear and
robust. To that end, we pull DMA and MSI cookies apart a little more,
mostly to clear up the ambiguity at domain teardown, then for clarity
(and to save a little space), move them into the union, whose ownership
we can then properly describe and enforce entirely unambiguously.

[nicolinc: rebase on latest tree; use prefix IOMMU_COOKIE_; merge unions
           in iommu_domain; add IOMMU_COOKIE_IOMMUFD for iommufd_hwpt]

Link: https://patch.msgid.link/r/1ace9076c95204bbe193ee77499d395f15f44b23.1742871535.git.nicolinc@nvidia.com
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index e93d2e918599..06cc14e9993d 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -41,6 +41,7 @@ struct iommu_dirty_ops;
 struct notifier_block;
 struct iommu_sva;
 struct iommu_dma_cookie;
+struct iommu_dma_msi_cookie;
 struct iommu_fault_param;
 struct iommufd_ctx;
 struct iommufd_viommu;
@@ -165,6 +166,15 @@ struct iommu_domain_geometry {
 	bool force_aperture;       /* DMA only allowed in mappable range? */
 };
 
+enum iommu_domain_cookie_type {
+	IOMMU_COOKIE_NONE,
+	IOMMU_COOKIE_DMA_IOVA,
+	IOMMU_COOKIE_DMA_MSI,
+	IOMMU_COOKIE_FAULT_HANDLER,
+	IOMMU_COOKIE_SVA,
+	IOMMU_COOKIE_IOMMUFD,
+};
+
 /* Domain feature flags */
 #define __IOMMU_DOMAIN_PAGING	(1U << 0)  /* Support for iommu_map/unmap */
 #define __IOMMU_DOMAIN_DMA_API	(1U << 1)  /* Domain for use in DMA-API
@@ -211,12 +221,12 @@ struct iommu_domain_geometry {
 
 struct iommu_domain {
 	unsigned type;
+	enum iommu_domain_cookie_type cookie_type;
 	const struct iommu_domain_ops *ops;
 	const struct iommu_dirty_ops *dirty_ops;
 	const struct iommu_ops *owner; /* Whose domain_alloc we came from */
 	unsigned long pgsize_bitmap;	/* Bitmap of page sizes in use */
 	struct iommu_domain_geometry geometry;
-	struct iommu_dma_cookie *iova_cookie;
 	int (*iopf_handler)(struct iopf_group *group);
 
 #if IS_ENABLED(CONFIG_IRQ_MSI_IOMMU)
@@ -224,10 +234,10 @@ struct iommu_domain {
 		      phys_addr_t msi_addr);
 #endif
 
-	union { /* Pointer usable by owner of the domain */
-		struct iommufd_hw_pagetable *iommufd_hwpt; /* iommufd */
-	};
-	union { /* Fault handler */
+	union { /* cookie */
+		struct iommu_dma_cookie *iova_cookie;
+		struct iommu_dma_msi_cookie *msi_cookie;
+		struct iommufd_hw_pagetable *iommufd_hwpt;
 		struct {
 			iommu_fault_handler_t handler;
 			void *handler_token;