Re: CONFIG_THUMB2_KERNEL=y boot failure after Spectre BHB fixes

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Christian Eggers <ceggers@arri.de>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	llvm@lists.linux.dev, Nathan Chancellor <nathan@kernel.org>
Subject: Re: CONFIG_THUMB2_KERNEL=y boot failure after Spectre BHB fixes
Date: Wed, 30 Mar 2022 17:36:55 +0100	[thread overview]
Message-ID: <YkSHJ65qGHO4bonJ@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAMj1kXGLehBkaG7-t5PZqN+32MS-5BDX-QGOe6ftZnPuNDKicg@mail.gmail.com>

On Wed, Mar 30, 2022 at 06:34:25PM +0200, Ard Biesheuvel wrote:
> On Wed, 30 Mar 2022 at 18:12, Russell King (Oracle)
> <linux@armlinux.org.uk> wrote:
> >
> > On Tue, Mar 22, 2022 at 06:49:17PM +0100, Christian Eggers wrote:
> > > Hi Nathan, hi Russel,
> > >
> > > I stumbled today over the same problem (no output on serial console
> > > with v5.15.28-rt36). During `git bisect`, I had also some commits
> > > where a few lines of output were visible.
> > >
> > > At commit 8d9d651ff227 ("ARM: use LOADADDR() to get load address of
> > > sections"), the system boots up to here:
> > >
> > > start_kernel()
> > > +--setup_arch()
> > >    +--paging_init()
> > >       +--devicemaps_init()
> > >          +--eary_trap_init(vectors_base = 0xC7FFE000)
> > >             +--copy_from_lma(vectors_base = 0xC7FFE000, __vectors_start=0x0, __vectors_end=0x20)
> > >                +--__memcpy()
> > >
> > >                copy_template.S:113
> > >                ldr8w   r1, r3, r4, r5, r6, r7, r8, ip, lr, abort=20f
> > >                r1 = 0
> > >
> > >
> > > With the final v5.15.28-rt36 I found out that the system boots fine
> > > after disabling CONFIG_HARDEN_BRANCH_HISTORY.
> > >
> > > Is there anything else I could analyze? My SoC system is a NXP i.MX6LL
> > > with a ARMv7 core. I have access to a JTAG debugger.
> >
> > I think this is already fixed in mainline. Commit:
> >
> > 6c7cb60bff7a ("ARM: fix Thumb2 regression")
> >
> 
> It's still broken - I sent a couple of patches on Monday, among which
> one to fix the boot issue with loop8 on Thumb2. The problem is 'b . +
> 4', which produces a narrow encoding, and so it skips the subsequent
> subs instruction and loops forever.

And what's the current status? Sorry, I've way too much email from the
last 2.5 weeks to find it myself.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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