From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 834FD22ACE3 for ; Tue, 22 Apr 2025 08:35:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745310924; cv=none; b=e0n1DjtHog5qElemHfYyYugJNxKrsX3cfeCeBTf3LFz2raJ3FFbFz4GGrM3d0x46OPW7jCOIqcDP9QUnNFX3AkFr/KTtxyGLLD5c3kf+Z/FsIC9wPcGscaCQWL1Yiq+M3jUTtUd1Vj4X85j9N2pOvZsA1/1zQFebHXZiD1L1SVQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745310924; c=relaxed/simple; bh=tkcz3fDoQtNMo4Zmg+sngA67GADtQkWp13qhVcacadk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=iF/Ec9AhWwy457iwPSULnLlw+HvtfAKfGJrxJuHnuePToT1a7N2oOULKjfEHVMjX5AQSmWpow0lCuwCljmHuDhC293RvrblfLaYz96B+wYqoO+FYZMjR65QziT8uA2gB7NXLxAYQz7Y5xJH2BAEYMa+ovPa9TseNrsJgNhgm/0c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=X7+8ljZa; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="X7+8ljZa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 457E8C4CEEA; Tue, 22 Apr 2025 08:35:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745310924; bh=tkcz3fDoQtNMo4Zmg+sngA67GADtQkWp13qhVcacadk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X7+8ljZag9MrMdygB/e5mTshdnVjmpMziL5L0xJEcDaZY8DYtpt7fNbFPgA/SVWxt 2Yh0hgP7jPhR4y4DTAfUd7sG7e6+xC2ORhALpoGls/i+F1610naxJf2JBqPnsH0vRo 3TI5FZu+7LSxVki7fAOtVyXq5W/yD/oiOLIoDrLDpIHtlv2u2BWt0N6DCLcXSWqZLf HFdXaNg1GpqjOxf3kjwOKadK3E2omKDA/UhFkZQPHIyvJUbuUdf1ddUoYVIB6g2X3x KtPOM60g96iMDCSmVxW/UHsImBJvRfb6qGIuTwccVssytmjoNmwxqxyfnb2ncw3Q+5 pZXUfVZwnSGlA== Date: Tue, 22 Apr 2025 11:35:17 +0300 From: Mike Rapoport To: Qu Wenruo Cc: Ingo Molnar , Borislav Petkov , Linux Memory Management List , LKML , Dave Hansen , x86-ml Subject: Re: Kernel 6.15-rc2 unable to boot on 32bit x86 with PAE Message-ID: References: <4599013d-bc74-4f81-9db7-070806ea9162@gmx.com> <20250418160515.GAaAJ4O2HnktVgmZ1v@fat_crate.local> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Apr 22, 2025 at 05:02:55PM +0930, Qu Wenruo wrote: > > > 在 2025/4/22 16:30, Ingo Molnar 写道: > > > > * Borislav Petkov wrote: > > > > > On Fri, Apr 18, 2025 at 08:31:23PM +0930, Qu Wenruo wrote: > > > > Hi, > > > > > > > > Recently I'm testing a situation where highmem is involved, thus I'm > > > > building the latest 32bit x86 with HIGHMEM and PAE, and run it inside a qemu > > > > VM. > > > > > > Does that fix it: > > > > > > https://git.kernel.org/tip/1e07b9fad022e0e02215150ca1e20912e78e8ec1 > > > > > > ? > > > > That commit caused other problems - the best fix we have right now is: > > > > https://git.kernel.org/tip/83b2d345e1786fdab96fc2b52942eebde125e7cd > > Thanks, I'll take a try again. > > But considering how rare 32bit + highmem systems are nowadays, I still have > one questions/concern: > > - How to make sure we really got highmems? > The kernel docs only mention that highmems need temporary mapping, > and proper kmap/kunmap() handling. > > But I still didn't have a straightforward idea of how to verify, > without adding manual ftrace events when a highmem page is hit. > > E.g. free only shows 3GB memory even if I enabled highmem + PAE. Without HIGHMEM it would be less than 900M. You can look for "HIGHMEM available" and "Memory: n/m available" in the kernel log to see how much highmem is there. > Since HIGHMEM64G is removed, I'd expect to get some values more like > 4G instead? There are some gaps under 4G, so it's surely less that 4G of usable memory there. > Thanks, > Qu -- Sincerely yours, Mike.