From 58b55c859ac00c6845b6aed8852c541bc204c935 Mon Sep 17 00:00:00 2001 From: Jean-Philippe Brucker Date: Wed, 12 Jun 2019 18:59:38 +0100 Subject: [PATCH] iommu: Add padding to struct iommu_fault Ease future extensions of struct iommu_fault_page_request and struct iommu_fault_unrecoverable by adding a few bytes of padding. That way, a new field can be added to either of these structures by simply introducing a new flag. To extend it after the size limit is reached, a new fault reporting structure will have to be negotiated with userspace. With 56 bytes of padding, the total size of iommu_fault is 64 bytes and fits in a cache line on a lot of contemporary machines, while providing 16 and 24 bytes of extension to structures iommu_fault_page_request and iommu_fault_unrecoverable respectively. Signed-off-by: Jean-Philippe Brucker Acked-by: Jacob Pan Reviewed-by: Eric Auger Signed-off-by: Joerg Roedel --- include/uapi/linux/iommu.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h index f45d8e9e59c3..fc00c5d4741b 100644 --- a/include/uapi/linux/iommu.h +++ b/include/uapi/linux/iommu.h @@ -106,6 +106,7 @@ struct iommu_fault_page_request { * @padding: reserved for future use (should be zero) * @event: fault event, when @type is %IOMMU_FAULT_DMA_UNRECOV * @prm: Page Request message, when @type is %IOMMU_FAULT_PAGE_REQ + * @padding2: sets the fault size to allow for future extensions */ struct iommu_fault { __u32 type; @@ -113,6 +114,7 @@ struct iommu_fault { union { struct iommu_fault_unrecoverable event; struct iommu_fault_page_request prm; + __u8 padding2[56]; }; };