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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 <jean-philippe.brucker@arm.com>
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Jean-Philippe Brucker 2019-06-12 18:59:38 +01:00 committed by Joerg Roedel
parent bf3255b3cf
commit 58b55c859a
1 changed files with 2 additions and 0 deletions
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2
include/uapi/linux/iommu.h
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@ -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];
};
};