Re: [Qemu-devel] [PATCHv2] spapr: Correct RAM size calculation for HPT resizing

[Greg Kurz <groug@kaod.org>]

On Wed, 11 Oct 2017 11:06:49 +1100
David Gibson <david@gibson.dropbear.id.au> 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 <david@gibson.dropbear.id.au>
> ---
>  hw/ppc/spapr_hcall.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Changes in v2:
>   * Also remove redundant initializer of current_ram_size
> 

* And use ram_size machine attribute instead of the ram_size global.

Reviewed-by: Greg Kurz <groug@kaod.org>


> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 8d72bb7c1c..0d59d1534d 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -472,7 +472,7 @@ static target_ulong h_resize_hpt_prepare(PowerPCCPU *cpu,
>      target_ulong flags = args[0];
>      int shift = args[1];
>      sPAPRPendingHPT *pending = spapr->pending_hpt;
> -    uint64_t current_ram_size = MACHINE(spapr)->ram_size;
> +    uint64_t current_ram_size;
>      int rc;
>  
>      if (spapr->resize_hpt == SPAPR_RESIZE_HPT_DISABLED) {
> @@ -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 = MACHINE(spapr)->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