Re: How to increase memory in a RISCV32 image? Stuck with 988MB

[Daniel Henrique Barboza]

On 4/18/23 08:10, Mikhail R. Gadelha wrote:
> Yeah, I mentioned in the email it doesn't even start with mem=4G...
>
> With lower values, e.g., mem=3G, the image starts but I'm limited to 988MB of 
> RAM.

QEMU doesn't make a distinction between 32 or 64 bits when setting the memory 
banks.


From Linux kernel arch/riscv/mm/init.c, early_mem():


        pr_notice("Memory limited to %lldMB\n", (u64)memory_limit >> 20);


'memory_limit' is defined in the same file in setup_vm() as:

        /*
         * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit
         * kernel, whereas for 64-bit kernel, the end of the virtual address
         * space is occupied by the modules/BPF/kernel mappings which reduces
         * the available size of the linear mapping.
         */
        memory_limit = KERN_VIRT_SIZE - (IS_ENABLED(CONFIG_64BIT) ? SZ_4G : 0);


So my educated guess here is that the kernel is capping the max memory for 32 
bits
to 988Mb, as you've pointed in your first email.


Thanks,


Daniel

> Em ter., 18 de abr. de 2023 às 04:42, Thomas Huth <thuth@redhat.com 
> <mailto:thuth@redhat.com>> escreveu:
>
>     On 17/04/2023 19.21, Mikhail R. Gadelha wrote:
>      > Hi qemu folks,
>      >
>      > I'm using yocto to generate a riscv32 image but qemu seems to be ignoring
>      > the -m argument from the command line and forcing the image to run with
>      > 988MB of RAM.
>      >
>      > Is there any way I can increase it to 4G?
>      >
>      > I'm using the following cmdline to start qemu:
>      >
>      > qemu-system-riscv32 -nographic -machine virt -m 4G -smp 8 -bios
>      > /home/mgadelha/tools/poky/build/tmp/deploy/images/qemuriscv32/fw_jump.elf
>      > -kernel 
> /home/mgadelha/tools/poky/build/tmp/deploy/images/qemuriscv32/Image
>      > -append "root=/dev/vda rw mem=4G" -drive
>
>     That "mem=4G" part of the -append option looks suspicious ... have you
>     already tried to boot without that, or to decrease it to a number that fits
>     into 32-bit, e.g. "mem=3G" ?
>
>        HTH,
>         Thomas
>
>      > 
> id=disk0,file=/home/mgadelha/tools/poky/build/tmp/deploy/images/qemuriscv32/core-image-full-cmdline-qemuriscv32-20230415202008.rootfs.ext4,if=none,format=raw
>  -device virtio-net-device,netdev=usernet -netdev 
> user,id=usernet,hostfwd=tcp::22222-:22 -device virtio-blk-device,drive=disk0 
> -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 
> -device virtio-tablet-pci -device virtio-keyboard-pci
>      >
>      > Well, it actually doesn't start if I use -m 4G, but any value lower than
>      > that is fine.
>      >
>      > Here's also the boot log: https://pastebin.com/b7ZEP659 
> <https://pastebin.com/b7ZEP659>
>      > <https://pastebin.com/b7ZEP659 <https://pastebin.com/b7ZEP659>>
>      >
>      > I see that the kernel prints:
>      >
>      > [    0.000000] Memory limited to 1024MB
>      >
>      > so maybe it's a kernel limitation rather than qemu?
>      >
>      > --
>      >
>      > Mikhail Ramalho.
>
>
>
> --
>
> Mikhail Ramalho.