linux-kernel - Re: [PATCH] x86: sgx: Don't track poisoned pages for reclaiming

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Message-ID: <4a1c8b84-d8ee-414a-bd6d-a8633302dab4@intel.com>
Date: Wed, 12 Feb 2025 10:18:11 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, Dave Hansen <dave.hansen@...el.com>
CC: Andrew Zaborowski <andrew.zaborowski@...el.com>, <x86@...nel.org>,
	<linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, "Thomas
 Gleixner" <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Ingo Molnar
	<mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, <balrogg@...il.com>
Subject: Re: [PATCH] x86: sgx: Don't track poisoned pages for reclaiming



On 12/02/2025 10:03 am, Jarkko Sakkinen wrote:
> On Tue, Feb 11, 2025 at 08:25:58AM -0800, Dave Hansen wrote:
>>> arch_memory_failure() but stay on sgx_active_page_list.
>>> page->poison is not checked in the reclaimer logic meaning that a page could be
>>> reclaimed and go through ETRACK, EBLOCK and EWB.  This can lead to the
>>> firmware receiving and MCE in one of those operations and going into
>>> "unbreakable shutdown" and triggering a kernel panic on remaining cores.
>>
>> This requires low-level SGX implementation knowledge to fully
>> understand. Both what "ETRACK, EBLOCK and EWB" are in the first place,
>> how they are involved in reclaim and also why EREMOVE doesn't lead to
>> the same fate.
> 
> Does it? [I'll dig up Intel SDM to check this]
> 

I just did. :-)

It seems EREMOVE only reads and updates the EPCM entry for the target 
EPC page but won't actually access that EPC page.