linux-kernel - Re: [PATCH v36 09/24] x86/sgx: Add __sgx_alloc_epc_page() and sgx_free_epc

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Date:   Thu, 06 Aug 2020 14:29:34 +0100
From:   Darren Kenny <darren.kenny@...cle.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, bp@...en8.de, cedric.xing@...el.com,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, 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
Subject: Re: [PATCH v36 09/24] x86/sgx: Add __sgx_alloc_epc_page() and
 sgx_free_epc_page()

On Thursday, 2020-07-16 at 16:52:48 +03, Jarkko Sakkinen wrote:
> Add __sgx_alloc_epc_page(), which iterates through EPC sections and borrows
> a page structure that is not used by anyone else. When a page is no longer
> needed it must be released with sgx_free_epc_page(). This function
> implicitly calls ENCLS[EREMOVE], which will return the page to the
> uninitialized state (i.e. not required from caller part).
>
> Acked-by: Jethro Beekman <jethro@...tanix.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>

Reviewed-by: Darren Kenny <darren.kenny@...cle.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 c5831e3db14a..97c6895fb6c9 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -83,6 +83,68 @@ 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);
> +
> +		if (page)
> +			return page;
> +	}
> +
> +	return ERR_PTR(-ENOMEM);
> +}
> +
> +/**
> + * sgx_free_epc_page() - Free an EPC page
> + * @page:	an EPC page
> + *
> + * Call EREMOVE for an EPC page and insert it back to the list of free pages.
> + */
> +void sgx_free_epc_page(struct sgx_epc_page *page)
> +{
> +	struct sgx_epc_section *section = sgx_get_epc_section(page);
> +	int ret;
> +
> +	ret = __eremove(sgx_get_epc_addr(page));
> +	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
> +		return;
> +
> +	spin_lock(&section->lock);
> +	list_add_tail(&page->list, &section->page_list);
> +	spin_unlock(&section->lock);
> +}
> +
>  static void __init sgx_free_epc_section(struct sgx_epc_section *section)
>  {
>  	struct sgx_epc_page *page;
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index dff4f5f16d09..fce756c3434b 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -49,4 +49,7 @@ static inline void *sgx_get_epc_addr(struct sgx_epc_page *page)
>  	return section->va + (page->desc & PAGE_MASK) - section->pa;
>  }
>  
> +struct sgx_epc_page *__sgx_alloc_epc_page(void);
> +void sgx_free_epc_page(struct sgx_epc_page *page);
> +
>  #endif /* _X86_SGX_H */
> -- 
> 2.25.1