linux-kernel - Re: [PATCH] x86/sgx: Fix deadloop in __sgx_alloc_epc

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Message-Id: <D3SJOVADFM48.JNOIOZJ0J6OE@kernel.org>
Date: Thu, 29 Aug 2024 19:44:13 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Aaron Lu" <aaron.lu@...el.com>, "Dave Hansen"
 <dave.hansen@...ux.intel.com>
Cc: <x86@...nel.org>, <linux-sgx@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, "Zhimin Luo" <zhimin.luo@...el.com>
Subject: Re: [PATCH] x86/sgx: Fix deadloop in __sgx_alloc_epc_page()

On Thu Aug 29, 2024 at 5:38 AM EEST, Aaron Lu wrote:
> When current node doesn't have a EPC section configured by firmware and
> all other EPC sections memory are used up, CPU can stuck inside the
> while loop in __sgx_alloc_epc_page() forever and soft lockup will happen.
> Note how nid_of_current will never equal to nid in that while loop because
                                                     ~~~~

Oh *that* while loop ;-) Please be more specific.

> nid_of_current is not set in sgx_numa_mask.
>
> Also worth mentioning is that it's perfectly fine for firmware to not
> seup an EPC section on a node. Setting an EPC section on each node can
> be good for performance but that's not a requirement functionality wise.

This lacks any description of what is done to __sgx_alloc_epc_page().

>
> Fixes: 901ddbb9ecf5 ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
> Reported-by: Zhimin Luo <zhimin.luo@...el.com>
> Tested-by: Zhimin Luo <zhimin.luo@...el.com>
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>

BR, Jarkko