On Saturday, 29 January 2022 7:08:17 AM AEDT Alex Sierra wrote:
[...]
> struct migrate_vma {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index cd137aedcfe5..d3cc3589e1e8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2264,7 +2264,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> if (is_writable_device_private_entry(entry))
> mpfn |= MIGRATE_PFN_WRITE;
> } else {
> - if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> + if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM) &&
> + !(migrate->flags &
> MIGRATE_VMA_SELECT_DEVICE_COHERENT))
> goto next;
> pfn = pte_pfn(pte);
> if (is_zero_pfn(pfn)) {
Sorry, but I still don't think this is quite right.
When specifying MIGRATE_VMA_SELECT_DEVICE_COHERENT we are looking for pages to
migrate from the device back to system memory. But as currently written I think
this can also select the zero pfn when MIGRATE_VMA_SELECT_DEVICE_COHERENT is
specified. As far as I know that can never point to device memory so migration
of a zero pfn should be also be skipped in that case.
We should only migrate the zero pfn if MIGRATE_VMA_SELECT_SYSTEM is specified.
> @@ -2273,6 +2274,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> goto next;
> }
> page = vm_normal_page(migrate->vma, addr, pte);
> + if (page && !is_zone_device_page(page) &&
> + !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> + goto next;
> + if (page && is_device_coherent_page(page) &&
> + (!(migrate->flags &
> MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> + page->pgmap->owner != migrate->pgmap_owner))
> + goto next;
> mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
> }
>
