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

[Igor Opaniuk]

Hello Ard,

Just a quick follow-up for this old thread,

I've again stumbled upon the same issue recently and it turned out
that I've already sent a fix for that here :)

Considering Heinrich's comment about memory granularity, does it still make
sense to land this patch? If not, what objections/suggestions do you
have in mind?

Thanks!

Regards,
Igor

On Thu, Feb 11, 2021 at 4:39 PM Igor Opaniuk <igor.opaniuk at foundries.io> wrote:
>
> Hi Heinrich,
>
> On Thu, Feb 11, 2021 at 5:34 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >
> > On 11.02.21 15:56, Ard Biesheuvel wrote:
> > > 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.
> > >
> >
> > $ qemu-system-arm -machine virt -cpu cortex-a15 -m 100005k \
> > -bios denx/u-boot.bin -nographic
> >
> > => fdt addr $fdt_addr
> > => fdt print /memory at 40000000
> > memory at 40000000 {
> >         reg = <0x00000000 0x40000000 0x00000000 0x061aa000>;
> >         device_type = "memory";
> > };
> >
> > Granularity seems to be 0x2000 = 8 KiB.
> I've just run some tests (including the mem=100005k ) with LPAE disabled
> and haven't faced any issues:
>
> $ cat .config | grep LPAE
> # CONFIG_ARMV7_LPAE is not set
>
> $ qemu-system-arm -machine virt -m 1057 -nographic -bios u-boot.bin
> U-Boot 2021.04-rc1-01218-g85e959f09c-dirty (Feb 11 2021 - 17:31:31 +0200)
>
> DRAM:  1 GiB
> Flash: 128 MiB
> ...
> =>
>
> $ qemu-system-arm -machine virt -m 1058 -nographic -bios u-boot.bin
>
> U-Boot 2021.04-rc1-01218-g85e959f09c-dirty (Feb 11 2021 - 17:31:31 +0200)
>
> DRAM:  1 GiB
> Flash: 128 MiB
> ...
> =>
>
> $ qemu-system-arm -machine virt -m 100005k -nographic -bios u-boot.bin
>
> U-Boot 2021.04-rc1-01218-g85e959f09c-dirty (Feb 11 2021 - 17:31:31 +0200)
> DRAM:  97.7 MiB
> Flash: 128 MiB
> ...
> =>
>
> >
> > Best regards
> >
> > Heinrich
>
> Regards,
> Igor
>
> --
> Best regards - Freundliche Grüsse - Meilleures salutations
>
> Igor Opaniuk
> Embedded Software Engineer
> T:  +380 938364067
> E: igor.opaniuk at foundries.io
> W: www.foundries.io



-- 
Best regards - Freundliche Grüsse - Meilleures salutations

Igor Opaniuk
Senior Software Engineer, Embedded & Security
E: igor.opaniuk at foundries.io
W: www.foundries.io