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Date: Mon, 29 Apr 2024 16:24:04 +0300
Message-Id: <D0WN15R16S1S.PRG8LSXA8470@kernel.org>
Cc: <mona.vij@intel.com>, <kailun.qin@intel.com>, <stable@vger.kernel.org>,
 =?utf-8?q?Marcelina_Ko=C5=9Bcielnicka?= <mwk@invisiblethingslab.com>
Subject: Re: [PATCH 1/2] x86/sgx: Resolve EAUG race where losing thread
 returns SIGBUS
From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Jarkko Sakkinen" <jarkko@kernel.org>, "Dmitrii Kuvaiskii"
 <dmitrii.kuvaiskii@intel.com>, <dave.hansen@linux.intel.com>,
 <kai.huang@intel.com>, <haitao.huang@linux.intel.com>,
 <reinette.chatre@intel.com>, <linux-sgx@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
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References: <20240429104330.3636113-1-dmitrii.kuvaiskii@intel.com>
 <20240429104330.3636113-2-dmitrii.kuvaiskii@intel.com>
 <D0WMM3MYQODE.3A89L7D6OVG3E@kernel.org>
 <D0WN0B2JL7N4.V0GPQWA79SJ5@kernel.org>
In-Reply-To: <D0WN0B2JL7N4.V0GPQWA79SJ5@kernel.org>

On Mon Apr 29, 2024 at 4:22 PM EEST, Jarkko Sakkinen wrote:
> On Mon Apr 29, 2024 at 4:04 PM EEST, Jarkko Sakkinen wrote:
> > > Fix these two bugs (1) by returning VM_FAULT_NOPAGE to the generic Li=
nux
> > > fault handler so that no signal is sent to userspace, and (2) by
> > > replacing sgx_encl_free_epc_page() with sgx_free_epc_page() so that n=
o
> > > EREMOVE is performed.
> >
> > What is the collateral damage caused by ENCLS[EREMOVE]?
>
> Have you measured cost of eremove on an empty page?
>
> I tried to lookup for a thread from lore because I have a faint memory
> that it was concluded that its cost irrelevant. Please correct if I'm
> wrong.

Also pseudocode for EREMOVE supports this as it just returns without
actually doing anything.

BR, Jarkko