Re: [PATCH v4 02/10] mm: add device coherent vma selection for memory migration

[Alistair Popple]

On Thursday, 27 January 2022 2:09:41 PM AEDT Alex Sierra wrote:

[...]

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 277562cd4cf5..2b3375e165b1 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;

This isn't correct as it allows zero pfn pages to be selected for migration
when they shouldn't be (ie. because MIGRATE_VMA_SELECT_SYSTEM isn't specified).

>   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 (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;
>   }
> 

[PATCH v4 02/10] mm: add device coherent vma selection for memory migration

[Alex Sierra]

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 277562cd4cf5..2b3375e165b1 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 (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;
}
-- 
2.32.0