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

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Message-ID: <Z60RsC1h94UdsjRb@kernel.org>
Date: Wed, 12 Feb 2025 23:25:04 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: "Huang, Kai" <kai.huang@...el.com>,
	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 Tue, Feb 11, 2025 at 03:31:54PM -0800, Dave Hansen wrote:
> On 2/11/25 13:18, Huang, Kai wrote:
> >>> 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.
> 
> Actually, now that I think about it even more, why would ETRACK or
> EBLOCK access the page itself? They seem superficially like they'd be
> metadata-only too.

Did a sanity check to SDM.

I think you're correct, and also there's zero rational reason them use
anything but EPCM (no legit reason to access payload itself).

BR, Jarkko