Re: [PATCH v40 09/24] x86/sgx: Add SGX page allocator functions

[Borislav Petkov]

On Wed, Nov 04, 2020 at 04:54:15PM +0200, Jarkko Sakkinen wrote:
> The previous patch initialized a simple SGX page allocator.  Add functions
> for runtime allocation and free.
> 
> This allocator and its algorithms are as simple as it gets.  They do a
> linear search across all EPC sections and find the first free page.  They
> are not NUMA aware and only hand out individual pages.  The SGX hardware
> does not support large pages, so something more complicated like a buddy
> allocator is unwarranted.
> 
> The free function (sgx_free_epc_page()) implicitly calls ENCLS[EREMOVE],
> which returns the page to the uninitialized state.  This ensures that the
> page is ready for use at the next allocation.
> 
> Acked-by: Jethro Beekman <jet...@fortanix.com>
> Reviewed-by: Darren Kenny <darren.ke...@oracle.com>
> Co-developed-by: Sean Christopherson <sean.j.christopher...@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 62 ++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/sgx.h  |  3 ++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 956055a0eff6..b9ac438a13a4 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -85,6 +85,68 @@ static bool __init sgx_page_reclaimer_init(void)
>       return true;
>  }
>  
> +static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct 
> sgx_epc_section *section)
> +{
> +     struct sgx_epc_page *page;
> +
> +     if (list_empty(&section->page_list))
> +             return NULL;
> +
> +     page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
> +     list_del_init(&page->list);
> +
> +     return page;
> +}
> +
> +/**
> + * __sgx_alloc_epc_page() - Allocate an EPC page
> + *
> + * Iterate through EPC sections and borrow a free EPC page to the caller. 
> When a
> + * page is no longer needed it must be released with sgx_free_epc_page().
> + *
> + * Return:
> + *   an EPC page,
> + *   -errno on error
> + */
> +struct sgx_epc_page *__sgx_alloc_epc_page(void)
> +{
> +     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];
> +             spin_lock(&section->lock);
> +             page = __sgx_alloc_epc_page_from_section(section);
> +             spin_unlock(&section->lock);

Something for a future cleanup: you can put that logic into
__sgx_alloc_epc_page_from_section() and simplify this one call site.

But not now - you can do that later or if v41 needs to be sent out...

Thx.

-- 
Regards/Gruss,
    Boris.

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