linux-kernel - Re: [PATCH v2 2/2] x86/sgx: Log information when a node lacks an EPC section

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Message-Id: <D3YF42L6VP2I.12ZOBQPIPQ2BA@kernel.org>
Date: Thu, 05 Sep 2024 17:24:59 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Aaron Lu" <aaron.lu@...el.com>, "Dave Hansen"
 <dave.hansen@...ux.intel.com>, "Kai Huang" <kai.huang@...el.com>
Cc: "Molina Sabido, Gerardo" <gerardo.molina.sabido@...el.com>, "Zhimin Luo"
 <zhimin.luo@...el.com>, <linux-sgx@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <x86@...nel.org>
Subject: Re: [PATCH v2 2/2] x86/sgx: Log information when a node lacks an
 EPC section

On Thu Sep 5, 2024 at 11:08 AM EEST, Aaron Lu wrote:
> For optimized performance, firmware typically distributes EPC sections
> evenly across different NUMA nodes. However, there are scenarios where
> a node may have both CPUs and memory but no EPC section configured. For
> example, in an 8-socket system with a Sub-Numa-Cluster=2 setup, there
> are a total of 16 nodes. Given that the maximum number of supported EPC
> sections is 8, it is simply not feasible to assign one EPC section to
> each node. This configuration is not incorrect - SGX will still operate
> correctly; it is just not optimized from a NUMA standpoint.
>
> For this reason, log a message when a node with both CPUs and memory
> lacks an EPC section. This will provide users with a hint as to why they
> might be experiencing less-than-ideal performance when running SGX
> enclaves.
>
> Suggested-by: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 694fcf7a5e3a..3a79105455f1 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -848,6 +848,13 @@ static bool __init sgx_page_cache_init(void)
>  		return false;
>  	}
>  
> +	for_each_online_node(nid) {
> +		if (!node_isset(nid, sgx_numa_mask) &&
> +		    node_state(nid, N_MEMORY) && node_state(nid, N_CPU))
> +			pr_info("node%d has both CPUs and memory but doesn't have an EPC section\n",
> +				nid);

Is this enough, or is there anything that would need to be done
automatically if this happens? With a tracepoint you could react to such
even but I'm totally fine with this.

> +	}
> +
>  	return true;
>  }
>  

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko