linux-kernel - Re: [PATCH 05/11] x86: remove HIGHMEM64G support

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Message-Id: <4a75978a-2368-4aab-bed6-ce44b6d3c323@app.fastmail.com>
Date: Sat, 12 Apr 2025 12:44:44 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Mike Rapoport" <rppt@...nel.org>, "Dave Hansen" <dave.hansen@...el.com>
Cc: "Arnd Bergmann" <arnd@...nel.org>, linux-kernel@...r.kernel.org,
 x86@...nel.org, "Thomas Gleixner" <tglx@...utronix.de>,
 "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>,
 "Linus Torvalds" <torvalds@...ux-foundation.org>,
 "Andy Shevchenko" <andy@...nel.org>, "Matthew Wilcox" <willy@...radead.org>,
 "Sean Christopherson" <seanjc@...gle.com>,
 "Davide Ciminaghi" <ciminaghi@...dd.com>,
 "Paolo Bonzini" <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 05/11] x86: remove HIGHMEM64G support

On Sat, Apr 12, 2025, at 12:05, Mike Rapoport wrote:
> On Fri, Apr 11, 2025 at 04:44:13PM -0700, Dave Hansen wrote:
>> Has anyone run into any problems on 6.15-rc1 with this stuff?
>> 
>> 0xf75fe000 is the mem_map[] entry for the first page >4GB. It obviously
>> wasn't allocated, thus the oops. Looks like the memblock for the >4GB
>> memory didn't get removed although the pgdats seem correct.
>
> That's apparently because of 6faea3422e3b ("arch, mm: streamline HIGHMEM
> freeing"). 
> Freeing of high memory was clamped to the end of ZONE_HIGHMEM which is 4G
> and after 6faea3422e3b there's no more clamping, so memblock_free_all()
> tries to free memory >4G as well.

Ah, I should have waited with my bisection, you found it first...

>> I'll dig into it some more. Just wanted to make sure there wasn't a fix
>> out there already.
>
> This should fix it.

Confirmed on 6.15-rc1.

     Arnd