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

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Date:   Thu, 5 Nov 2020 16:08:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jethro Beekman <jethro@...tanix.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com, kai.huang@...el.com,
        kai.svahn@...el.com, kmoy@...gle.com, ludloff@...gle.com,
        luto@...nel.org, nhorman@...hat.com, npmccallum@...hat.com,
        puiterwijk@...hat.com, rientjes@...gle.com, tglx@...utronix.de,
        yaozhangx@...gle.com, mikko.ylinen@...el.com
Subject: Re: [PATCH v40 09/24] x86/sgx: Add SGX page allocator functions

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 <jethro@...tanix.com>
> Reviewed-by: Darren Kenny <darren.kenny@...cle.com>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.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.

https://people.kernel.org/tglx/notes-about-netiquette