Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Received-SPF: Fail (protection.outlook.com: domain of arri.de does not
 designate 217.111.95.7 as permitted sender) receiver=protection.outlook.com;
 client-ip=217.111.95.7; helo=mta.arri.de;
From:   Christian Eggers <ceggers@arri.de>
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>,
        Ard Biesheuvel <ardb@kernel.org>
CC:     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 19:32:59 +0200
Message-ID: <10062923.nUPlyArG6x@localhost.localdomain>
Organization: Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
In-Reply-To: <CAMj1kXFcrG6TrSU+KcmXCVM7ZWZ2fMjiN8c_dtEwxBugJS_UAQ@mail.gmail.com>
References: <YipOoAaBIHjeCKOq@dev-arch.thelio-3990X> <YkSHJ65qGHO4bonJ@shell.armlinux.org.uk> <CAMj1kXFcrG6TrSU+KcmXCVM7ZWZ2fMjiN8c_dtEwxBugJS_UAQ@mail.gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Mar 2022 17:33:00.9793
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 78b0a886-6fcf-4450-881f-08da127356a5
X-MS-Exchange-CrossTenant-Id: e6a73a5a-614d-4c51-b3e3-53b660a9433a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=e6a73a5a-614d-4c51-b3e3-53b660a9433a;Ip=[217.111.95.7];Helo=[mta.arri.de]
X-MS-Exchange-CrossTenant-AuthSource: HE1EUR02FT070.eop-EUR02.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR07MB7674
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RDNS_NONE,
	SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no
	version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wednesday, 30 March 2022, 18:45:18 CEST, Ard Biesheuvel wrote:
> On Wed, 30 Mar 2022 at 18:37, Russell King (Oracle)
> <linux@armlinux.org.uk> wrote:
> >
> > 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.
> >
> 
> https://lore.kernel.org/linux-arm-kernel/20220328134714.205342-1-ardb@kernel.org/
> 
> Nobody bothered to respond yet, I can drop the first two in the patch
> tracker if you like.

I just switched to v5.15.31-rt38 which already includes
6c7cb60bff7a ("ARM: fix Thumb2 regression")

This kernel boots fine now, even with CONFIG_HARDEN_BRANCH_HISTORY=y. After
applying the patch series from Ard, the system still boots fine. 

I haven't any understanding what these patches do. Is there anything I shall
test?

regards
Christian