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Date:   Fri, 30 Aug 2019 16:25:13 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Sasha Levin <sashal@kernel.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, x86-ml <x86@kernel.org>
Subject: Re: [PATCH AUTOSEL 5.2 51/76] x86/boot/compressed/64: Fix boot on
 machines with broken E820 table
Message-ID: <20190830132513.emsgzw6nty2blfv5@box>
References: <20190829181311.7562-1-sashal@kernel.org>
 <20190829181311.7562-51-sashal@kernel.org>
 <20190829221723.eicsws3q7gp6nx37@box>
 <20190830120638.GW5281@sasha-vm>
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On Fri, Aug 30, 2019 at 08:06:38AM -0400, Sasha Levin wrote:
> On Fri, Aug 30, 2019 at 01:17:23AM +0300, Kirill A. Shutemov wrote:
> > On Thu, Aug 29, 2019 at 02:12:46PM -0400, Sasha Levin wrote:
> > > From: "Kirill A. Shutemov" <kirill@shutemov.name>
> > > 
> > > [ Upstream commit 0a46fff2f9108c2c44218380a43a736cf4612541 ]
> > > 
> > > BIOS on Samsung 500C Chromebook reports very rudimentary E820 table that
> > > consists of 2 entries:
> > > 
> > >   BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] usable
> > >   BIOS-e820: [mem 0x00000000fffff000-0x00000000ffffffff] reserved
> > > 
> > > It breaks logic in find_trampoline_placement(): bios_start lands on the
> > > end of the first 4k page and trampoline start gets placed below 0.
> > > 
> > > Detect underflow and don't touch bios_start for such cases. It makes
> > > kernel ignore E820 table on machines that doesn't have two usable pages
> > > below BIOS_START_MAX.
> > > 
> > > Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > > Signed-off-by: Borislav Petkov <bp@suse.de>
> > > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > > Cc: Ingo Molnar <mingo@redhat.com>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: x86-ml <x86@kernel.org>
> > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=203463
> > > Link: https://lkml.kernel.org/r/20190813131654.24378-1-kirill.shutemov@linux.intel.com
> > > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > 
> > Please postpone backporting the patch (and into other trees). There's a
> > fixup for it:
> > 
> > http://lore.kernel.org/r/20190826133326.7cxb4vbmiawffv2r@box
> 
> Sure. Should I just queue it up for a week or two later (along with the
> fixes), or do you want to let me know when?

You can queue it up later (two weeks is fine) once the fixup hit Linus' tree.

-- 
 Kirill A. Shutemov