[PATCH v1] qemu-arm: round down memory to multiple of 2MB

[Ard Biesheuvel]

On Thu, 11 Feb 2021 at 15:18, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 11.02.21 13:04, Igor Opaniuk wrote:
> > From: Igor Opaniuk <igor.opaniuk at foundries.io>
> >
> > When LPAE is enabled, 1:1 mapping is created using 2 MB blocks.
> > In case amount of memory provided to QEMU is not multiple
> > of 2 MB, round down the amount of available memory to avoid hang
> > during MMU initialization.
> >
> > How to reproduce:
> > qemu-system-arm -machine virt -m 1058 -nographic -bios u-boot.bin - boots
> > qemu-system-arm -machine virt -m 1057 -nographic -bios u-boot.bin - hangs
> >
> > DRAM:  1 GiB
> > initcall: 60011df8
> > initcall: 60011904
> > New Stack Pointer is: 80fffe90
> > initcall: 60011a20
> > initcall: 60011bcc
> > initcall: 60011bd4
> > initcall: 600119b4
> > Relocation Offset is: 22042000
> > Relocating to 82042000, new gd at 81001ed0, sp at 80fffe90
> > initcall: 60011b8c
> > initcall: 82053ea0
> > initcall: 82053ea8
> > initcall: 60012040 (relocated to 82054040)
> > dram_bank_mmu_setup: bank: 0
> > --- hang here during mmu init ---
> >
> > Fixes: 3fa914af82("arm: qemu: implement enable_caches()")
> > Signed-off-by: Igor Opaniuk <igor.opaniuk at foundries.io>
> >
> > ---
> >
> >  board/emulation/qemu-arm/qemu-arm.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
> > index aa68bef469..841dd7af0e 100644
> > --- a/board/emulation/qemu-arm/qemu-arm.c
> > +++ b/board/emulation/qemu-arm/qemu-arm.c
> > @@ -84,6 +84,18 @@ int dram_init(void)
> >       if (fdtdec_setup_mem_size_base() != 0)
> >               return -EINVAL;
> >
> > +     /*
> > +      * When LPAE is enabled (ARMv7),
> > +      * 1:1 mapping is created using 2 MB blocks.
> > +      *
> > +      * In case amount of memory provided to QEMU
> > +      * is not multiple of 2 MB, round down the amount
> > +      * of available memory to avoid hang during MMU
> > +      * initialization.
> > +      */
> > +     if (CONFIG_IS_ENABLED(ARMV7_LPAE))
> > +             gd->ram_size -= (gd->ram_size % 0x200000);
>
> Is the problem LPAE specific?
> Couldn't you provoke same problem using an odd memory size without LPAE,
> e.g qemu-system-arm -m 536870908 (512 MiB - 4)?
>

The above value means 512 GiB - 4 MiB, so that shouldn't be a problem.
I don't think QEMU's -m option takes fractional megabyte values.