On 29.06.22 05:54, Alex Sierra wrote: > With DEVICE_COHERENT, we'll soon have vm_normal_pages() return > device-managed anonymous pages that are not LRU pages. Although they > behave like normal pages for purposes of mapping in CPU page, and for > COW. They do not support LRU lists, NUMA migration or THP. > > Callers to follow_page that expect LRU pages, are also checked for > device zone pages due to DEVICE_COHERENT type. Can we rephrase that to (because zeropage) "Callers to follow_page() currently don't expect ZONE_DEVICE pages, however, with DEVICE_COHERENT we might now return ZONE_DEVICE. Check for ZONE_DEVICE pages in applicable users of follow_page() as well." [...] > /* > diff --git a/mm/memory.c b/mm/memory.c > index 7a089145cad4..e18555af9024 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -624,6 +624,13 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > if (is_zero_pfn(pfn)) > return NULL; > if (pte_devmap(pte)) > +/* > + * NOTE: New uers of ZONE_DEVICE will not set pte_devmap() and will have s/uers/users/ > + * refcounts incremented on their struct pages when they are inserted into > + * PTEs, thus they are safe to return here. Legacy ZONE_DEVICE pages that set > + * pte_devmap() do not have refcounts. Example of legacy ZONE_DEVICE is > + * MEMORY_DEVICE_FS_DAX type in pmem or virtio_fs drivers. > + */ [...] > diff --git a/mm/mprotect.c b/mm/mprotect.c > index ba5592655ee3..e034aae2a98b 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -95,7 +95,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, > continue; > > page = vm_normal_page(vma, addr, oldpte); > - if (!page || PageKsm(page)) > + if (!page || is_zone_device_page(page) || PageKsm(page)) > continue; > > /* Also skip shared copy-on-write pages */ In -next/-mm there is now an additional can_change_pte_writable() that calls vm_normal_page() -- added by me. I assume that that is indeed fine because we can simply map device coherent pages writable. Besides the nits, LGTM Acked-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
