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

Kirill A. Shutemov
2018-06-14T15:57:21Z

On Wed, Jun 13, 2018 at 06:07:40PM +0000, Dave Hansen wrote:
> 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?

Right. I'll update commit message.

> > 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.

You are right. I'll measure for the next iteration.

> > --- 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?

Yes, it compiles.

Before I reorganized macros around alloc_page_vma(), the argument was
ignored for non-NUMA systems. NUMA on Alpha marked BROKEN and never
enabled.

> > +#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.

There's no new argument. I've just unified alloc_hugepage_vma() codepath
for NUMA and non-NUMA.

But sure I'll split it into a separate 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.

Sure.

> > 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.

Got it.

> > 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

Makes sense.

> > 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?

No. I asked to implement encrypted page allocation as a wrappers on top of
existing routines.

> > +#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. :)

Okay.

> > + 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?

We already have alloc_pages_vma() for NUMA. See mm/mempolicy.c.

> > +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?

I'll see what I can do here.

Not sure if a wrapper will be cleaner for a reader: we need to return two
values new gfp_mask and page_need_zeroing.

> > + 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. :)
>

--
Kirill A. Shutemov