On Tuesday, 16 November 2021 6:30:19 AM AEDT Alex Sierra wrote:
> This case is used to migrate pages from device memory, back to system
> memory. Device coherent type memory is cache coherent from device and CPU
> point of view.
>
> Signed-off-by: Alex Sierra
> ---
> v2:
> condition added when migrations from device coherent pages.
> ---
> include/linux/migrate.h | 1 +
> mm/migrate.c| 9 +++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index c8077e936691..e74bb0978f6f 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -138,6 +138,7 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
> enum migrate_vma_direction {
> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
> + MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2,
> };
>
> struct migrate_vma {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f74422a42192..166bfec7d85e 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2340,8 +2340,6 @@ 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))
> - goto next;
> pfn = pte_pfn(pte);
> if (is_zero_pfn(pfn)) {
> mpfn = MIGRATE_PFN_MIGRATE;
> @@ -2349,6 +2347,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> goto next;
> }
> page = vm_normal_page(migrate->vma, addr, pte);
> + if (!is_zone_device_page(page) &&
> + !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> + goto next;
> + if (is_zone_device_page(page) &&
> + (!(migrate->flags &
> MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> + page->pgmap->owner != migrate->pgmap_owner))
> + goto next;
Thanks Alex, couple of comments on this:
1. vm_normal_page() can return NULL so you need to add a check for
page == NULL otherwise the call to is_zone_device_page(NULL) will crash.
2. The check for a coherent device page is too indirect. Being explicit and
using is_zone_device_coherent_page() instead would make it more direct and
obvious, particularly for developers who may not immediately realise that
device-private pages should never have pte_present() entries.
> mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
> }
>
