Hi Jean,
On 6/12/19 7:59 PM, Jean-Philippe Brucker wrote:
> 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 <[email protected]>
Reviewed-by: Eric Auger <[email protected]>
Thanks
Eric
> ---
> 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
> @@ -105,15 +105,17 @@ struct iommu_fault_page_request {
> * @type: fault type from &enum iommu_fault_type
> * @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;
> __u32 padding;
> union {
> struct iommu_fault_unrecoverable event;
> struct iommu_fault_page_request prm;
> + __u8 padding2[56];
> };
> };
>
> /**
>
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