linux-kernel - Re: [PATCH] x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc

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Date:   Sun, 21 Feb 2021 16:54:33 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     haitao.huang@...el.com, dan.j.williams@...el.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Add a basic NUMA allocation scheme to
 sgx_alloc_epc_page()

> +/* 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.