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SubjectRe: [PATCH 3/4] iommu/amd: Do not sync on page size changes
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On 2021-05-02 07:59, Nadav Amit wrote:
> From: Nadav Amit <namit@vmware.com>
>
> Some IOMMU architectures perform invalidations regardless of the page
> size. In such architectures there is no need to sync when the page size
> changes or to regard pgsize when making interim flush in
> iommu_iotlb_gather_add_page().
>
> Add a "ignore_gather_pgsize" property for each IOMMU-ops to decide
> whether gather's pgsize is tracked and triggers a flush.

I've objected before[1], and I'll readily object again ;)

I still think it's very silly to add a bunch of indirection all over the
place to make a helper function not do the main thing it's intended to
help with. If you only need trivial address gathering then it's far
simpler to just implement trivial address gathering. I suppose if you
really want to you could factor out another helper to share the 5 lines
of code which ended up in mtk-iommu (see commit f21ae3b10084).

Robin.

[1]
https://lore.kernel.org/linux-iommu/49bae447-d662-e6cf-7500-ab78e3b75dc4@arm.com/

> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Jiajun Cao <caojiajun@vmware.com>
> Cc: iommu@lists.linux-foundation.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> drivers/iommu/amd/iommu.c | 1 +
> include/linux/iommu.h | 3 ++-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index b8cabbbeed71..1849b53f2149 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2215,6 +2215,7 @@ const struct iommu_ops amd_iommu_ops = {
> .put_resv_regions = generic_iommu_put_resv_regions,
> .is_attach_deferred = amd_iommu_is_attach_deferred,
> .pgsize_bitmap = AMD_IOMMU_PGSIZES,
> + .ignore_gather_pgsize = true,
> .flush_iotlb_all = amd_iommu_flush_iotlb_all,
> .iotlb_sync = amd_iommu_iotlb_sync,
> .def_domain_type = amd_iommu_def_domain_type,
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 32d448050bf7..1fb2695418e9 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -284,6 +284,7 @@ struct iommu_ops {
> int (*def_domain_type)(struct device *dev);
>
> unsigned long pgsize_bitmap;
> + bool ignore_gather_pgsize;
> struct module *owner;
> };
>
> @@ -508,7 +509,7 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
> * a different granularity, then sync the TLB so that the gather
> * structure can be rewritten.
> */
> - if (gather->pgsize != size ||
> + if ((gather->pgsize != size && !domain->ops->ignore_gather_pgsize) ||
> end + 1 < gather->start || start > gather->end + 1) {
> if (gather->pgsize)
> iommu_iotlb_sync(domain, gather);
>

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