linux-kernel - Re: [PATCH] cxl/acpi: Verify CHBS length for CXL2.0

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Message-ID: <67e5544237027_13cb29432@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Date: Thu, 27 Mar 2025 09:36:02 -0400
From: Dan Williams <dan.j.williams@...el.com>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>, Ira Weiny
	<ira.weiny@...el.com>, "linux-cxl@...r.kernel.org"
	<linux-cxl@...r.kernel.org>
CC: Jonathan Cameron <jonathan.cameron@...wei.com>, Dave Jiang
	<dave.jiang@...el.com>, Alison Schofield <alison.schofield@...el.com>,
	"Vishal Verma" <vishal.l.verma@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/acpi: Verify CHBS length for CXL2.0

Zhijian Li (Fujitsu) wrote:
> 
> 
> On 27/03/2025 11:44, Ira Weiny wrote:
> > Li Zhijian wrote:
> >> Per CXL Spec r3.1 Table 9-21, both CXL1.1 and CXL2.0 have defined their
> >> own length, verify it to avoid an invalid CHBS
> > 
> > 
> > I think this looks fine.  But did a platform have issues with this?  
> 
> Not really, actually, I discovered it while reviewing the code and
> CXL specification.
> 
> Currently, this issue arises only when I inject an incorrect length
> via QEMU environment. Our hardware does not experience this problem.
> 
> 
> > Does this need to be backported?
> I remain neutral :)

What does the kernel do with this invalid CHBS from QEMU? I would be
happy to let whatever bad effect from injecting a corrupted CHBS just
happen because there are plenty of ways for QEMU to confuse the kernel
even if the table lengths are correct.

Unless it has real impact I would rather not touch the kernel for every
possible way that QEMU can make a mistake.

I.e. if it was a widespread problem that affected multiple QEMU users by
default then maybe. Just your local test gone awry? Maybe not.