linux-kernel - Re: [PATCH v4] x86/mm/ident_map: On UV systems, use gbpages only where full GB page should be mapped.

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Date: Fri, 29 Mar 2024 09:15:38 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Pavin Joseph <me@...injoseph.com>
Cc: Steve Wahl <steve.wahl@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	Linux regressions mailing list <regressions@...ts.linux.dev>,
	stable@...r.kernel.org, Eric Hagberg <ehagberg@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, Sarah Brofeldt <srhb@....dk>,
	Russ Anderson <rja@....com>, Dimitri Sivanich <sivanich@....com>,
	Hou Wenlong <houwenlong.hwl@...group.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Yuntao Wang <ytcoode@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v4] x86/mm/ident_map: On UV systems, use gbpages only
 where full GB page should be mapped.


* Pavin Joseph <me@...injoseph.com> wrote:

> On 3/29/24 12:45, Ingo Molnar wrote:
> > Does the 'nogbpages' kernel command line option fail on these systems
> > even outside of kexec (ie. regular boot), or only in combination with
> > kexec?
> 
> Original reporter here, using nogbpages allows for normal bootup, but 
> kexec fails with it on my two similar systems.

Just to clarify, we have the following 3 upstream (and soon to be upstream) versions:

 v1: pre-d794734c9bbf kernels
 v2: d794734c9bbf x86/mm/ident_map: Use gbpages only where full GB page should be mapped.
 v3: c567f2948f57 Revert "x86/mm/ident_map: Use gbpages only where full GB page should be mapped."

Where v1 and v3 ought to be the same in behavior.

So how does the failure matrix look like on your systems? Is my 
understanding accurate:


           regular boot  | regular kexec | nogbpages boot | nogbpages kexec boot
 ------------------------|---------------------------------------------------
 v1:       OK            | OK            | OK             | FAIL
 v2:       OK            | FAIL          | FAIL           | FAIL

?

Thanks,

	Ingo