Re: [PATCH v4 1/3] iommu: Sort out domain user data

From: Nicolin Chen
Date: Fri Mar 07 2025 - 00:57:56 EST


Hi Baolu,

On Fri, Mar 07, 2025 at 10:28:20AM +0800, Baolu Lu wrote:
> On 3/7/25 05:00, Nicolin Chen wrote:
> > From: Robin Murphy<robin.murphy@xxxxxxx>

Robin had remarks here, wrt iommu_set_fault_handler():

> > 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.
[...]
> > @@ -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;
>
> My feeling is that IOMMU_COOKIE_FAULT_HANDLER isn't exclusive to
> IOMMU_COOKIE_DMA_IOVA; both might be used for kernel DMA with a paging
> domain.
>
> I am afraid that iommu_set_fault_handler() doesn't work anymore as the
> domain's cookie type has already been set to IOMMU_COOKIE_DMA_IOVA.

All three existing iommu_set_fault_handler() callers in the tree
are UNMANAGED domain users:
5 451 drivers/gpu/drm/msm/msm_iommu.c <<msm_iommu_gpu_new>>
iommu_set_fault_handler(iommu->domain, msm_fault_handler, iommu);
6 453 drivers/infiniband/hw/usnic/usnic_uiom.c <<usnic_uiom_alloc_pd>>
iommu_set_fault_handler(pd->domain, usnic_uiom_dma_fault, NULL);
8 118 drivers/remoteproc/remoteproc_core.c <<rproc_enable_iommu>>
iommu_set_fault_handler(domain, rproc_iommu_fault, rproc);

On the other hand, IOMMU_COOKIE_DMA_IOVA is a private cookie for
dma-iommu only.

So, I think we are probably fine?

Thanks
Nicolin