get_user_pages and pinning

[Cengiz Can]

Hello Sadanand

On January 2, 2021 3:39:08 PM GMT+03:00, Sadanand Warrier <sadanandwarrier at gmail.com> wrote:
>Folks
>   Since Linux uses lazy evaluation with respect to allocating memory
>what happens if a user process allocates memory using malloc in excess
>of say 8 or nine pages and calls a device ioctl and passes the user
>space pointer to it to be used to pin pages using get_user_pages().

I don't have an answer to your question because your sentences are too long and I couldn't understand the thing you are asking. 

>This buffer is to be used for a dma read from a device.
>What happens if the memory isn't actually allocated (no initialization
>with memset or calloc etc. and all PTEs are pointing to some zero
>filled page) and there is no IOMMU?
>Thanks
>
>S

 Please use punctuation marks as termination points and keep your sentences shorter for better responses from any community. 

Thank you