Re: [PATCHv3 04/17] mm/page_alloc: Handle allocation for encrypted memory

Dave Hansen
2018-06-13T18:07:45Z

On 06/12/2018 07:39 AM, Kirill A. Shutemov wrote:
> For encrypted memory, we need to allocated pages for a specific
> encryption KeyID.

"allocate" ^

> There are two cases when we need to allocate a page for encryption:
>
> - Allocation for an encrypted VMA;
>
> - Allocation for migration of encrypted page;
>
> The first case can be covered within alloc_page_vma().

... because we know the KeyID from the VMA?

> The second case requires few new page allocation routines that would
> allocate the page for a specific KeyID.
>
> Encrypted page has to be cleared after KeyID set. This is handled by

"An encrypted page has ... "

This description lacks a description of the performance impact of the
approach in this patch both when allocating encrypted and normal pages.

> --- a/arch/alpha/include/asm/page.h
> +++ b/arch/alpha/include/asm/page.h
> @@ -18,7 +18,7 @@ extern void clear_page(void *page);
> #define clear_user_page(page, vaddr, pg) clear_page(page)
>
> #define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
> - alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vmaddr)
> + alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
> #define __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE

Does this compile? Wouldn't "vmaddr" be undefined?

> +#define alloc_hugepage_vma(gfp_mask, vma, addr, order) \
> + alloc_pages_vma(gfp_mask, order, vma, addr, numa_node_id(), true)

The argument addition should be broken out into a preparatory patch.

> extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);
> extern unsigned long get_zeroed_page(gfp_t gfp_mask);
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index f2b4abbca55e..6da504bad841 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -38,9 +38,11 @@ static inline struct page *new_page_nodemask(struct page *page,
> unsigned int order = 0;
> struct page *new_page = NULL;
>
> - if (PageHuge(page))
> + if (PageHuge(page)) {
> + WARN_ON(page_keyid(page));
> return alloc_huge_page_nodemask(page_hstate(compound_head(page)),
> preferred_nid, nodemask);
> + }

Comment on the warning, please.

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 9ac49ef17b4e..00bccbececea 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -920,22 +920,24 @@ static void migrate_page_add(struct page *page, struct list_head *pagelist,
> /* page allocation callback for NUMA node migration */
> struct page *alloc_new_node_page(struct page *page, unsigned long node)
> {
> - if (PageHuge(page))
> + if (PageHuge(page)) {
> + WARN_ON(page_keyid(page));
> return alloc_huge_page_node(page_hstate(compound_head(page)),
> node);

Comments, please.

> @@ -2012,9 +2014,16 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
> {
> struct mempolicy *pol;
> struct page *page;
> - int preferred_nid;
> + bool zero = false;
> + int keyid, preferred_nid;
> nodemask_t *nmask;
>
> + keyid = vma_keyid(vma);
> + if (keyid && gfp & __GFP_ZERO) {
> + zero = true;
> + gfp &= ~__GFP_ZERO;
> + }

I totally read that wrong.

"zero" needs to be named: "page_need_zeroing".

It also badly needs a comment.

> pol = get_vma_policy(vma, addr);
>
> if (pol->mode == MPOL_INTERLEAVE) {
> @@ -2057,6 +2066,8 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
> page = __alloc_pages_nodemask(gfp, order, preferred_nid, nmask);
> mpol_cond_put(pol);
> out:
> + if (page && keyid)
> + prep_encrypted_page(page, order, keyid, zero);
> return page;
> }

I'd just have prep_encrypted_page() do the keyid-0 opt-out of the prep
work. It'll be less to patch when you

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8c0af0f7cab1..eb8dea219dcb 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1847,7 +1847,7 @@ static struct page *alloc_misplaced_dst_page(struct page *page,
> int nid = (int) data;
> struct page *newpage;
>
> - newpage = __alloc_pages_node(nid,
> + newpage = __alloc_pages_node_keyid(nid, page_keyid(page),
> (GFP_HIGHUSER_MOVABLE |
> __GFP_THISNODE | __GFP_NOMEMALLOC |
> __GFP_NORETRY | __GFP_NOWARN) &

I thought folks asked you not to change all of the calling conventions
across the page allocator. It seems like you're still doing that,
though. A reviewer might think you've ignored their earlier feedback.
Did you?

> +#ifndef CONFIG_NUMA
> +struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
> + struct vm_area_struct *vma, unsigned long addr,
> + int node, bool hugepage)
> +{
> + struct page *page;
> + bool zero = false;
> + int keyid = vma_keyid(vma);
> +
> + if (keyid && (gfp_mask & __GFP_ZERO)) {

Please at least do your parenthesis consistently. :)

> + zero = true;
> + gfp_mask &= ~__GFP_ZERO;
> + }
> +
> + page = alloc_pages(gfp_mask, order);
> + if (page && keyid)
> + prep_encrypted_page(page, order, keyid, zero);
> +
> + return page;
> +}
> +#endif

I'm also confused by the #ifdef. What is it for?

> +struct page * __alloc_pages_node_keyid(int nid, int keyid,
> + gfp_t gfp_mask, unsigned int order)
> +{
> + struct page *page;
> + bool zero = false;
> +
> + VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
> + VM_WARN_ON(!node_online(nid));
> +
> + if (keyid && (gfp_mask & __GFP_ZERO)) {
> + zero = true;
> + gfp_mask &= ~__GFP_ZERO;
> + }

OK, so this is the third time I've seen that pattern. Are you *sure*
you don't want to consolidate the sites?

> + page = __alloc_pages(gfp_mask, order, nid);
> + if (page && keyid)
> + prep_encrypted_page(page, order, keyid, zero);
> +
> + return page;
> +}
> +
> #ifdef CONFIG_LOCKDEP
> struct lockdep_map __fs_reclaim_map =
> STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map);
> @@ -4396,6 +4439,26 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
> }
> EXPORT_SYMBOL(__alloc_pages_nodemask);
>
> +struct page *
> +__alloc_pages_nodemask_keyid(gfp_t gfp_mask, unsigned int order,
> + int preferred_nid, nodemask_t *nodemask, int keyid)
> +{
> + struct page *page;
> + bool zero = false;
> +
> + if (keyid && (gfp_mask & __GFP_ZERO)) {
> + zero = true;
> + gfp_mask &= ~__GFP_ZERO;
> + }

Fourth one. :)