> From: Christian Borntraeger
> Sent: Friday, February 7, 2020 7:39 PM
>
> From: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
>
> With the introduction of protected KVM guests on s390 there is now a
> concept of inaccessible pages. These pages need to be made accessible
> before the host can access them.
>
> While cpu accesses will trigger a fault that can be resolved, I/O
> accesses will just fail. We need to add a callback into architecture
> code for places that will do I/O, namely when writeback is started or
> when a page reference is taken.
What about hooking the callback to DMA API ops?
>
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> ---
> include/linux/gfp.h | 6 ++++++
> mm/gup.c | 2 ++
> mm/page-writeback.c | 1 +
> 3 files changed, 9 insertions(+)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index e5b817cb86e7..be2754841369 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -485,6 +485,12 @@ static inline void arch_free_page(struct page *page,
> int order) { }
> #ifndef HAVE_ARCH_ALLOC_PAGE
> static inline void arch_alloc_page(struct page *page, int order) { }
> #endif
> +#ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
> +static inline int arch_make_page_accessible(struct page *page)
> +{
> + return 0;
> +}
> +#endif
>
> struct page *
> __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int
> preferred_nid,
> diff --git a/mm/gup.c b/mm/gup.c
> index 7646bf993b25..a01262cd2821 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -257,6 +257,7 @@ static struct page *follow_page_pte(struct
> vm_area_struct *vma,
> page = ERR_PTR(-ENOMEM);
> goto out;
> }
> + arch_make_page_accessible(page);
> }
> if (flags & FOLL_TOUCH) {
> if ((flags & FOLL_WRITE) &&
> @@ -1870,6 +1871,7 @@ static int gup_pte_range(pmd_t pmd, unsigned
> long addr, unsigned long end,
>
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
>
> + arch_make_page_accessible(page);
> SetPageReferenced(page);
> pages[*nr] = page;
> (*nr)++;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2caf780a42e7..0f0bd14571b1 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2806,6 +2806,7 @@ int __test_set_page_writeback(struct page *page,
> bool keep_write)
> inc_lruvec_page_state(page, NR_WRITEBACK);
> inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> }
> + arch_make_page_accessible(page);
> unlock_page_memcg(page);
> return ret;
>
> --
> 2.24.0
