Re: [Qemu-devel] [PATCH] ppc/pnv: Warn when using -initrd and low ram

[Cédric Le Goater]

On 16/07/2019 06:56, Joel Stanley wrote:
> When booting with the default amount of RAM the powernv machine will
> load the initrd above the top of RAM and cause the Linux kernel to crash
> when it attempts to access the initrd:
> 
>   Linux/PowerPC load:
>   Finalizing device tree... flat tree at 0x202770c0
>   [    0.070476] nvram: Failed to find or create lnx,oops-log partition, err 
> -28
>   [    0.073270] nvram: Failed to initialize oops partition!
>   [    0.156302] BUG: Unable to handle kernel data access at 
> 0xc000000060000000
>   [    0.158009] Faulting instruction address: 0xc000000001002e5c
>   cpu 0x0: Vector: 300 (Data Access) at [c00000003d1e3870]
>       pc: c000000001002e5c: unpack_to_rootfs+0xdc/0x2f0
>       lr: c000000001002df4: unpack_to_rootfs+0x74/0x2f0
>       sp: c00000003d1e3b00
>      msr: 9000000002009033
>      dar: c000000060000000
>    dsisr: 40000000
>     current = 0xc00000003d1c0000
>     paca    = 0xc000000001320000       irqmask: 0x03   irq_happened: 0x01
>       pid   = 1, comm = swapper/0
>   Linux version 5.2.0-10292-g040e2e618374 (joel@voyager) (gcc version 8.3.0 
> (Debian 8.3.0-2)) #1 SMP Tue Jul 16 13:50:32 ACST 2019
>   enter ? for help
>   [c00000003d1e3bb0] c000000001003c90 populate_rootfs+0x84/0x1dc
>   [c00000003d1e3c40] c00000000000f494 do_one_initcall+0x88/0x1d0
>   [c00000003d1e3d10] c000000001000fc4 kernel_init_freeable+0x24c/0x250
>   [c00000003d1e3db0] c00000000000f7a0 kernel_init+0x1c/0x150
>   [c00000003d1e3e20] c00000000000b8a4 ret_from_kernel_thread+0x5c/0x78
> 
> Provide a helpful message for users so they don't go reporting bugs to
> kernel developers.
> 
> Signed-off-by: Joel Stanley <address@hidden>
> ---
> We could solve this in other ways, such as warn when loading the initrd
> outside of RAM, or load it within the known boundaries or RAM, but after
> hitting this myself I wanted to start the discussion.

We should also increase : 

    mc->default_ram_size = 1 * GiB;

to 2 or 4 GiB. I always use 4.

> Signed-off-by: Joel Stanley <address@hidden>
> ---
>  hw/ppc/pnv.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index bd4531c82260..bbd596ab9eca 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -649,6 +649,13 @@ static void pnv_init(MachineState *machine)


at the beginning of this routine we have :

    /* allocate RAM */
    if (machine->ram_size < (1 * GiB)) {
        warn_report("skiboot may not work with < 1GB of RAM");
    }

and we should exit instead. 

>      /* load initrd */
>      if (machine->initrd_filename) {
> +        if (machine->ram_size <= (1.5 * GiB)) {
> +            /* INITRD_LOAD_ADDR is at 1.5GB, so we require at least that 
> much RAM
> +             * when specifying the initrd on the command line */
> +            warn_report("initrd load requires > %ld MB of RAM",
> +                    INITRD_LOAD_ADDR / MiB);
> +        }

Shouldn't we take into account the initrd size also ? I don't know if it is 
relevant as it can be compressed.

>          pnv->initrd_base = INITRD_LOAD_ADDR;
>          pnv->initrd_size = load_image_targphys(machine->initrd_filename,
>                                    pnv->initrd_base, INITRD_MAX_SIZE);
>