Re: [PATCH 08/14] mm/hmm: cleanup special vma handling (VM_SPECIAL)

[John Hubbard]

On 03/16/2018 12:14 PM, jglisse@xxxxxxxxxx wrote:
> From: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> 
> Special vma (one with any of the VM_SPECIAL flags) can not be access by
> device because there is no consistent model accross device drivers on
> those vma and their backing memory.
> 
> This patch directly use hmm_range struct for hmm_pfns_special() argument
> as it is always affecting the whole vma and thus the whole range.
> 
> It also make behavior consistent after this patch both hmm_vma_fault()
> and hmm_vma_get_pfns() returns -EINVAL when facing such vma. Previously
> hmm_vma_fault() returned 0 and hmm_vma_get_pfns() return -EINVAL but
> both were filling the HMM pfn array with special entry.
> 

Hi Jerome,

This seems correct. 

<snip>

> @@ -486,6 +478,14 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
>  	return 0;
>  }
>  
> +static void hmm_pfns_special(struct hmm_range *range)
> +{
> +	unsigned long addr = range->start, i = 0;
> +
> +	for (; addr < range->end; addr += PAGE_SIZE, i++)
> +		range->pfns[i] = HMM_PFN_SPECIAL;
> +}

Silly nit: the above would read more naturally, like this:

	unsigned long addr, i = 0;

	for (addr = range->start; addr < range->end; addr += PAGE_SIZE, i++)
		range->pfns[i] = HMM_PFN_SPECIAL;

Either way,

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

thanks,
-- 
John Hubbard
NVIDIA