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

Dave Hansen
2021-02-22T00:55:33Z

> +/* 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.

> /*
> * 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].

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.

> 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.

> + } 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.

> + 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.