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SubjectRe: [PATCH 08/14] mm/hmm: cleanup special vma handling (VM_SPECIAL)
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On 03/16/2018 12:14 PM, jglisse@redhat.com wrote:
> From: Jérôme Glisse <jglisse@redhat.com>
>
> 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@nvidia.com>

thanks,
--
John Hubbard
NVIDIA

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