linux-kernel - Re: [PATCH] riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping

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Message-ID: <CAHVXubikF36Tc19vv9osVz3ZvEyKXk-+74YBpPAZQpSt+vFkQw@mail.gmail.com>
Date:   Tue, 4 Jul 2023 15:16:42 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Song Shuai <suagrfillet@...il.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Start of DRAM should at least be aligned on PMD
 size for the direct mapping

On Tue, Jul 4, 2023 at 2:26 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> Hey Alex,
>
> On Tue, Jul 04, 2023 at 02:18:37PM +0200, Alexandre Ghiti wrote:
> > So that we do not end up mapping the whole linear mapping using 4K
> > pages, which is slow at boot time, and also very likely at runtime.
> >
> > So make sure we align the start of DRAM on a PMD boundary.
> >
> > Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>
> Obviously correct me if I am wrong here, but was this not reported by
> Song Shuai as a regression?
> Accordingly, should this not have Reported-by, Closes/Link & Fixes tags?

Sure we should add the reported by from Song as he did the proper report :)

Reported-by: Song Shuai <suagrfillet@...il.com>
Closes: https://lore.kernel.org/linux-riscv/20230625140931.1266216-1-songshuaishuai@tinylab.org/

And yes sorry, I thought it was there before, but it was actually when
I retrieved the first 2MB that the problem appeared, so:

Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")

Thanks!

>
> Cheers,
> Conor.
>
> > ---
> >  arch/riscv/mm/init.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 4fa420faa780..4a43ec275c6d 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -214,8 +214,13 @@ static void __init setup_bootmem(void)
> >       memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
> >
> >       phys_ram_end = memblock_end_of_DRAM();
> > +
> > +     /*
> > +      * Make sure we align the start of the memory on a PMD boundary so that
> > +      * at worst, we map the linear mapping with PMD mappings.
> > +      */
> >       if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> > -             phys_ram_base = memblock_start_of_DRAM();
> > +             phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
> >
> >       /*
> >        * In 64-bit, any use of __va/__pa before this point is wrong as we
> > --
> > 2.39.2
> >