linux-kernel - Re: [PATCH v6 08/14] riscv: move boot alternatives to a slightly earlier position

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Date:   Wed, 23 Mar 2022 17:51:16 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org, wefu@...hat.com,
        liush@...winnertech.com, guoren@...nel.org, atishp@...shpatra.org,
        anup@...infault.org, drew@...gleboard.org,
        Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
        wens@...e.org, maxime@...no.tech, gfavor@...tanamicro.com,
        andrea.mondelli@...wei.com, behrensj@....edu, xinhaoqu@...wei.com,
        huffman@...ence.com, mick@....forth.gr,
        allen.baum@...erantotech.com, jscheid@...tanamicro.com,
        rtrauben@...il.com, samuel@...lland.org, cmuellner@...ux.com,
        philipp.tomsich@...ll.eu
Subject: Re: [PATCH v6 08/14] riscv: move boot alternatives to a slightly earlier position

Am Dienstag, 8. März 2022, 01:47:23 CET schrieb Palmer Dabbelt:
> On Wed, 09 Feb 2022 04:37:54 PST (-0800), heiko@...ech.de wrote:
> > Move the application of boot alternatives to soc_early_init().
> > This allows to catch more generic cases of code needing patches
> > than doing it in smp_prepare_boot_cpu() and also makes it actually
> > work if CONFIG_SMP is disabled for whatever reason.
> >
> > The position is chosen mainly as it is before the actual soc early
> > init runs but also already allows accessing the devicetree
> > via fdt_* functions.
> 
> I think this is OK, but it warrants testing on the K210 -- specifically 
> the system is in an odd state before soc_early_init (IIRC some of memory 
> doesn't work right) so I'm always a bit worried about calling stuff 
> there.  I don't have a K210 (or at least a working one), so I'm not 
> going to be able to test it.

just to finalize this partial thread, v7 and onward doesn't move
the alternative-application this early but instead actually behind
fill_hwcaps to be able to read available extensions.

So nothing to do for this - for people reading along, and me if
I don't remember this in the future ;-)

> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >  arch/riscv/kernel/head.S    | 2 ++
> >  arch/riscv/kernel/smpboot.c | 2 --
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 2363b43312fc..0e1bb97f9749 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -10,6 +10,7 @@
> >  #include <asm/thread_info.h>
> >  #include <asm/page.h>
> >  #include <asm/pgtable.h>
> > +#include <asm/alternative.h>
> >  #include <asm/csr.h>
> >  #include <asm/cpu_ops_sbi.h>
> >  #include <asm/hwcap.h>
> > @@ -341,6 +342,7 @@ clear_bss_done:
> >  	call kasan_early_init
> >  #endif
> >  	/* Start the kernel */
> > +	call apply_boot_alternatives
> >  	call soc_early_init
> >  	tail start_kernel
> >
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index a6d13dca1403..f1e4948a4b52 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -32,7 +32,6 @@
> >  #include <asm/sections.h>
> >  #include <asm/sbi.h>
> >  #include <asm/smp.h>
> > -#include <asm/alternative.h>
> >
> >  #include "head.h"
> >
> > @@ -41,7 +40,6 @@ static DECLARE_COMPLETION(cpu_running);
> >  void __init smp_prepare_boot_cpu(void)
> >  {
> >  	init_cpu_topology();
> > -	apply_boot_alternatives();
> >  }
> >
> >  void __init smp_prepare_cpus(unsigned int max_cpus)
>