linux-kernel - Re: [PATCH 1/4] x86/sgx: Add total number of EPC pages

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Message-ID: <Z98yki-gH4ewlpbP@kernel.org>
Date: Sat, 22 Mar 2025 23:58:42 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Elena Reshetova <elena.reshetova@...el.com>
Cc: dave.hansen@...el.com, linux-sgx@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	asit.k.mallick@...el.com, vincent.r.scarlata@...el.com,
	chongc@...gle.com, erdemaktas@...gle.com, vannapurve@...gle.com,
	dionnaglaze@...gle.com, bondarn@...gle.com, scott.raynor@...el.com
Subject: Re: [PATCH 1/4] x86/sgx: Add total number of EPC pages

On Fri, Mar 21, 2025 at 02:34:40PM +0200, Elena Reshetova wrote:
> In order to successfully execute ENCLS[EUPDATESVN], EPC must be empty.
> SGX already has a variable sgx_nr_free_pages that tracks free
> EPC pages. Add a new variable, sgx_nr_total_pages, that will keep
> track of total number of EPC pages. It will be used in subsequent
> patch to change the sgx_nr_free_pages into sgx_nr_used_pages and
> allow an easy check for an empty EPC.

First off, remove "in subsequent patch".

What does "change sgx_nr_free_pages into sgx_nr_used_pages" mean?

> 
> Note: The serialization for sgx_nr_total_pages is not needed because
> the variable is only updated during the initialization and there's no
> concurrent access.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 8ce352fc72ac..d5df67dab247 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -33,6 +33,7 @@ static LIST_HEAD(sgx_active_page_list);
>  static DEFINE_SPINLOCK(sgx_reclaimer_lock);
>  
>  static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
> +static unsigned long sgx_nr_total_pages;
>  
>  /* Nodes with one or more EPC sections. */
>  static nodemask_t sgx_numa_mask;
> @@ -648,6 +649,8 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
>  	}
>  
> +	sgx_nr_total_pages += nr_pages;
> +
>  	return true;
>  }
>  
> -- 
> 2.45.2
> 

BR, Jarkko