Re: [PATCH v2] hw: riscv: Allow large kernels to boot by moving the initrd further away in RAM

[Alexandre Ghiti]

On Tue, Feb 6, 2024 at 9:39 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
>
>
> On 2/6/24 12:40, Alexandre Ghiti wrote:
> > Currently, the initrd is placed at 128MB, which overlaps with the kernel
> > when it is large (for example syzbot kernels are). From the kernel side,
> > there is no reason we could not push the initrd further away in memory
> > to accommodate large kernels, so move the initrd at 512MB when possible.
> >
> > The ideal solution would have been to place the initrd based on the
> > kernel size but we actually can't since the bss size is not known when
> > the image is loaded by load_image_targphys_as() and the initrd would
> > then overlap with this section.
> >
> > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> > ---
>
> Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Thanks for your help!

Alex

>
> >
> > Changes in v2:
> > - Fix typos in commit log (Daniel) and title
> > - Added to the commit log why using the kernel size does not work
> >    (Daniel)
> >
> >   hw/riscv/boot.c | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
> > index 0ffca05189..9a367af2fa 100644
> > --- a/hw/riscv/boot.c
> > +++ b/hw/riscv/boot.c
> > @@ -188,13 +188,13 @@ static void riscv_load_initrd(MachineState *machine, 
> > uint64_t kernel_entry)
> >        * kernel is uncompressed it will not clobber the initrd. However
> >        * on boards without much RAM we must ensure that we still leave
> >        * enough room for a decent sized initrd, and on boards with large
> > -     * amounts of RAM we must avoid the initrd being so far up in RAM
> > -     * that it is outside lowmem and inaccessible to the kernel.
> > -     * So for boards with less  than 256MB of RAM we put the initrd
> > -     * halfway into RAM, and for boards with 256MB of RAM or more we put
> > -     * the initrd at 128MB.
> > +     * amounts of RAM, we put the initrd at 512MB to allow large kernels
> > +     * to boot.
> > +     * So for boards with less than 1GB of RAM we put the initrd
> > +     * halfway into RAM, and for boards with 1GB of RAM or more we put
> > +     * the initrd at 512MB.
> >        */
> > -    start = kernel_entry + MIN(mem_size / 2, 128 * MiB);
> > +    start = kernel_entry + MIN(mem_size / 2, 512 * MiB);
> >
> >       size = load_ramdisk(filename, start, mem_size - start);
> >       if (size == -1) {