Re: [PATCH] x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()

Jarkko Sakkinen
2021-02-23T19:18:18Z

On Sun, Feb 21, 2021 at 04:54:33PM -0800, Dave Hansen wrote:
> > +/* Nodes with one or more EPC sections. */
> > +static nodemask_t sgx_numa_mask;
>
> I'd also add that this is for optimization only.
>
> > +/* Array of lists of EPC sections for each NUMA node. */
> > +struct list_head *sgx_numa_nodes;
>
> I'd much prefer:
>
> /*
> * Array with one list_head for each possible NUMA node. Each
> * list contains all the sgx_epc_section's which are on that
> * node.
> */
>
> Otherwise, it's hard to imagine what this structure looks like.

OK.

> > /*
> > * These variables are part of the state of the reclaimer, and must be accessed
> > * with sgx_reclaimer_lock acquired.
> > @@ -473,6 +479,26 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct sgx_epc_sec
> > return page;
> > }
> >
> > +static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
> > +{
> > + struct sgx_epc_section *section;
> > + struct sgx_epc_page *page;
> > +
> > + if (WARN_ON_ONCE(nid < 0 || nid >= MAX_NUMNODES))
> > + return NULL;
> > +
> > + if (!node_isset(nid, sgx_numa_mask))
> > + return NULL;
> > +
> > + list_for_each_entry(section, &sgx_numa_nodes[nid], section_list) {
> > + page = __sgx_alloc_epc_page_from_section(section);
> > + if (page)
> > + return page;
> > + }
> > +
> > + return NULL;
> > +}
> > +
> > /**
> > * __sgx_alloc_epc_page() - Allocate an EPC page
> > *
> > @@ -485,13 +511,17 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct sgx_epc_sec
> > */
> > struct sgx_epc_page *__sgx_alloc_epc_page(void)
> > {
> > + int current_nid = numa_node_id();
> > struct sgx_epc_section *section;
> > struct sgx_epc_page *page;
> > int i;
> >
> > + page = __sgx_alloc_epc_page_from_node(current_nid);
> > + if (page)
> > + return page;
>
> Comments, please.
>
> /* Try to allocate EPC from the current node, first: */
>
> then:
>
> /* Search all EPC sections, ignoring locality: */
>
> > for (i = 0; i < sgx_nr_epc_sections; i++) {
> > section = &sgx_epc_sections[i];
> > -
> > page = __sgx_alloc_epc_page_from_section(section);
> > if (page)
> > return page;
>
> This still has the problem that it exerts too much pressure on the
> low-numbered sgx_epc_sections[]. If a node's sections are full, it
> always tries to go after sgx_epc_sections[0].

I have a better idea. See below.

> It can be in another patch, but I think the *minimal* thing we can do
> here for a NUMA allocator is to try to at least balance the allocations.
>
> Instead of having a for-each-section loop, I'd make it for-each-node ->
> for-each-section. Something like:
>
> for (i = 0; i < num_possible_nodes(); i++) {
> node = (numa_node_id() + i) % num_possible_nodes()
>
> if (!node_isset(nid, sgx_numa_mask))
> continue;
>
> list_for_each_entry(section, &sgx_numa_nodes[nid],
> section_list) {
> __sgx_alloc_epc_page_from_section(section)
> }
> }
>
> Then you have a single loop instead of a "try local then a fall back".
>
> Also, that "node++" thing might be able to use next_online_node().
>
> > @@ -665,8 +695,12 @@ static bool __init sgx_page_cache_init(void)
> > {
> > u32 eax, ebx, ecx, edx, type;
> > u64 pa, size;
> > + int nid;
> > int i;
> >
> > + nodes_clear(sgx_numa_mask);
> > + sgx_numa_nodes = kmalloc_array(MAX_NUMNODES, sizeof(*sgx_numa_nodes), GFP_KERNEL);
>
> MAX_NUMNODES will always be the largest compile-time constant. That's
> 4k, IIRC. num_possible_nodes() might be as small as 1 if NUMA is off.

Right.

> > for (i = 0; i < ARRAY_SIZE(sgx_epc_sections); i++) {
> > cpuid_count(SGX_CPUID, i + SGX_CPUID_EPC, &eax, &ebx, &ecx, &edx);
> >
> > @@ -690,6 +724,22 @@ static bool __init sgx_page_cache_init(void)
> > }
> >
> > sgx_nr_epc_sections++;
> > +
> > + nid = numa_map_to_online_node(phys_to_target_node(pa));
> > +
> > + if (nid == NUMA_NO_NODE) {
> > + pr_err(FW_BUG "unable to map EPC section %d to online node.\n", nid);
> > + nid = 0;
>
> Could we dump out the physical address there? I think that's even more
> informative than a section number.

Yes.

> > + } else if (WARN_ON_ONCE(nid < 0 || nid >= MAX_NUMNODES)) {
> > + nid = 0;
> > + }
>
> I'm not sure we really need to check for these. If we're worried about
> the firmware returning these, I'd expect numa_map_to_online_node() to
> sanity check them for us.

Yes, let's remove it.

> > + if (!node_isset(nid, sgx_numa_mask)) {
> > + INIT_LIST_HEAD(&sgx_numa_nodes[nid]);
> > + node_set(nid, sgx_numa_mask);
> > + }
> > +
> > + list_add_tail(&sgx_epc_sections[i].section_list, &sgx_numa_nodes[nid]);
> > }
> >
> > if (!sgx_nr_epc_sections) {
> > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> > index 5fa42d143feb..4bc31bc4bacf 100644
> > --- a/arch/x86/kernel/cpu/sgx/sgx.h
> > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> > @@ -45,6 +45,7 @@ struct sgx_epc_section {
> > spinlock_t lock;
> > struct list_head page_list;
> > unsigned long free_cnt;
> > + struct list_head section_list;
>
> Maybe name this numa_section_list.

Instead, let's just:

1. Have a global sgx_free_epc_list and remove sgx_epc_section.
Pages from this are allocated from this in LIFO fashion.
2. Instead add struct list_head node_list and use that for node
associated pages.
3. Replace 'int section' with 'int node'.

This will remove one layer of abstraction and provide better fallback
scheme.

E.g. allocate:

1. Check node_list of current node.
2. As a fallback check sgx_free_epc_list.
3. list_del() for two lists.

/Jarkko