Re: [PATCH v2 7/7] iommu: Turn iova_cookie to dma-iommu private pointer

On Wed, Feb 26, 2025 at 01:36:10PM -0400, Jason Gunthorpe wrote:

On Tue, Feb 25, 2025 at 06:25:27PM -0800, Nicolin Chen wrote:

quoted

On Fri, Feb 21, 2025 at 10:39:59AM -0400, Jason Gunthorpe wrote:

quoted

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 99dd72998cb7f7..082274e8ba6a3d 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h

@@ -1534,12 +1534,16 @@ void iommu_debugfs_setup(void);
 static inline void iommu_debugfs_setup(void) {}
 #endif
 
-#ifdef CONFIG_IOMMU_DMA
+#if defined(CONFIG_IOMMU_DMA) && IS_ENABLED(CONFIG_IRQ_MSI_IOMMU)
 int iommu_get_msi_cookie(struct iommu_domain *domain, dma_addr_t base);
+void iommu_put_msi_cookie(struct iommu_domain *domain);
 #else /* CONFIG_IOMMU_DMA */
 static inline int iommu_get_msi_cookie(struct iommu_domain *domain, dma_addr_t base)
 {
-	return -ENODEV;
+	return 0;

Should we keep the -ENODEV here for !CONFIG_IOMMU_DMA?

My feeling was if the system doesn't have an IRQ driver that needs
MSI_IOMMU but does have a IOMMU driver that reports SW_MSI reserved
regions then iommufd/vfio should not fail.

OK, I see. But we are also changing the behavior for the
!CONFIG_IOMMU_DMA configuration, in which case all other iommu
functions seem to return -ENODEV. And I assume we would need a
justification for such a change?

Perhaps, this can be explicit, just to keep the consistency:
	/* NOP if IOMMU driver reports SW_MSI reserved regions */
	return IS_ENABLED(CONFIG_IOMMU_DMA) ? 0 : -ENODEV;

I don't think it is realistic that we'd ever hit this return.

Yea, the only caller is VFIO, where there are quite a few IOMMU
functions calls before reaching to this one. So, it would have
been just returned with any -ENODEV prior.

Thanks
Nicolin