Re: [Qemu-devel] [PATCH] spapr: Correct RAM size calculation for HPT resizing

[Greg Kurz]

On Wed, 11 Oct 2017 00:21:59 +1100
David Gibson <address@hidden> wrote:

> In order to prevent the guest from forcing the allocation of large amounts
> of qemu memory (or host kernel memory, in the case of KVM HV), we limit
> the size of Hashed Page Table (HPT) it is allowed to allocated, based on
> its RAM size.
> 
> However, the current calculation is not correct: it only adds up the size
> of plugged memory, ignoring the base memory size.  This patch corrects it.
> 
> While we're there, use get_plugged_memory_size() instead of directly
> calling pc_existing_dimms_capacity().  The only difference is that it
> will abort on failure, which is right: a failure here indicates something
> wrong within qemu.
> 
> Signed-off-by: David Gibson <address@hidden>
> ---
>  hw/ppc/spapr_hcall.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 8d72bb7c1c..06af1b15c0 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -494,7 +494,7 @@ static target_ulong h_resize_hpt_prepare(PowerPCCPU *cpu,
>          return H_PARAMETER;
>      }
>  
> -    current_ram_size = pc_existing_dimms_capacity(&error_fatal);
> +    current_ram_size = ram_size + get_plugged_memory_size();

current_ram_size is initialized earlier in this function:

    uint64_t current_ram_size = MACHINE(spapr)->ram_size;

which is is initialized to ram_size in vl.c. Why not doing:

    current_ram_size += get_plugged_memory_size();

?

>  
>      /* We only allow the guest to allocate an HPT one order above what
>       * we'd normally give them (to stop a small guest claiming a huge