Re: [PATCH v2] x86/sgx: Hack in idea for allocating from local EPC node when possible

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Wed, May 13, 2020 at 10:10:36PM -0700, Sean Christopherson wrote:
> Allocate EPC from the local node when possible.  There is no new NUMA
> enumeration for EPC.  Because EPC is carved out of RAM on bare metal,
> the sections are naturally covered by the existing ACPI SRAT entries,
> i.e. can be found by querying the kernel's NUMA info.
> 
> Keep the per-section tracking to simplify iterating over all sections
> and reverse lookups given an EPC page.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> 
> I like this version a lot more.  Far less clever and doesn't assume
> anything about number of EPC sections vs. NUMA nodes.
> 
> As before, compile tested only.
> 
> For folks (especially non-Intel people) who may be confused, this is a
> less-than-an-RFC patch to frame in an idea for adding basic NUMA awareness
> for EPC sections without (yet) supporting full mempolicy stuff.
> 
>  arch/x86/kernel/cpu/sgx/main.c    | 95 +++++++++++++++++++++++++------
>  arch/x86/kernel/cpu/sgx/reclaim.c |  6 +-
>  arch/x86/kernel/cpu/sgx/sgx.h     |  6 +-
>  3 files changed, 84 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 5ce77e5546766..3128b4fa5ff4f 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -11,7 +11,15 @@
>  #include "driver.h"
>  #include "encls.h"
>  
> -struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
> +struct sgx_epc_node {
> +	struct sgx_epc_section sections[SGX_MAX_EPC_SECTIONS];
> +	int nr_sections;
> +};
> +
> +static struct sgx_epc_node sgx_epc_nodes[MAX_NUMNODES];
> +static int sgx_nr_epc_nodes;
> +
> +struct sgx_epc_section *sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
>  int sgx_nr_epc_sections;
>  
>  static struct sgx_epc_page *__sgx_try_alloc_page(struct sgx_epc_section *section)
> @@ -28,23 +36,15 @@ static struct sgx_epc_page *__sgx_try_alloc_page(struct sgx_epc_section *section
>  	return page;
>  }
>  
> -/**
> - * sgx_try_alloc_page() - Allocate an EPC page
> - *
> - * Try to grab a page from the free EPC page list.
> - *
> - * Return:
> - *   a pointer to a &struct sgx_epc_page instance,
> - *   -errno on error
> - */
> -struct sgx_epc_page *sgx_try_alloc_page(void)
> +static struct sgx_epc_page *sgx_try_alloc_page_node(int nid)
>  {
> +	struct sgx_epc_node *node = &sgx_epc_nodes[nid];
>  	struct sgx_epc_section *section;
>  	struct sgx_epc_page *page;
>  	int i;
>  
> -	for (i = 0; i < sgx_nr_epc_sections; i++) {
> -		section = &sgx_epc_sections[i];
> +	for (i = 0; i < node->nr_sections; i++) {
> +		section = &node->sections[i];
>  		spin_lock(&section->lock);
>  		page = __sgx_try_alloc_page(section);
>  		spin_unlock(&section->lock);
> @@ -53,6 +53,41 @@ struct sgx_epc_page *sgx_try_alloc_page(void)
>  			return page;
>  	}
>  
> +	return NULL;
> +}
> +
> +/**
> + * sgx_try_alloc_page() - Allocate an EPC page
> + *
> + * Try to grab a page from the free EPC page list.
> + *
> + * Return:
> + *   a pointer to a &struct sgx_epc_page instance,
> + *   -errno on error
> + */
> +struct sgx_epc_page *sgx_try_alloc_page(void)
> +{
> +	struct sgx_epc_page *page;
> +	int nid = numa_node_id();

This means that CONFIG_NUMA is not really needed.

/Jarkko