From: Nicolin Chen Date: Wed, 3 Jun 2026 21:26:55 +0000 (-0700) Subject: iommu: Avoid copying the user array twice in the full-array copy helper X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e28bee5b445178390d63f7a93a5a219063c6434e;p=thirdparty%2Flinux.git iommu: Avoid copying the user array twice in the full-array copy helper iommu_copy_struct_from_full_user_array() copies a whole user array into a kernel buffer. In the common case, where user entry_len equals destination entry size, it takes a fast path and copies the whole array with a single copy_from_user(). That fast path does not return, so it falls through into the item-by-item copy_struct_from_user() loop and copies every entry a second time. For an equal entry_len that loop is just a copy_from_user() of the same bytes, so the whole array is copied twice for no benefit. Return right after the bulk copy. The per-item loop then runs only on the slow path, where entry_len differs and each entry needs size adaption. Fixes: 4f2e59ccb698 ("iommu: Add iommu_copy_struct_from_full_user_array helper") Link: https://patch.msgid.link/r/6c9eca4ff584cb977661e97799ac6fe934e7f51c.1780521606.git.nicolinc@nvidia.com Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Nicolin Chen Reviewed-by: Lu Baolu Signed-off-by: Jason Gunthorpe --- diff --git a/include/linux/iommu.h b/include/linux/iommu.h index e587d4ac4d331..6957144263793 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -547,6 +547,7 @@ iommu_copy_struct_from_full_user_array(void *kdst, size_t kdst_entry_size, user_array->entry_num * user_array->entry_len)) return -EFAULT; + return 0; } /* Copy item by item */