Re: [Qemu-devel] [PATCH v10 10/10] hw/arm/virt: Bump the 255GB initial RAM limit

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 28 Feb 2019 16:03:24 +0100
Eric Auger <eric.auger@redhat.com> wrote:

> Now we have the extended memory map (high IO regions beyond the
> scalable RAM) and dynamic IPA range support at KVM/ARM level
> we can bump the legacy 255GB initial RAM limit. The actual maximum
> RAM size now depends on the physical CPU and host kernel, in
> accelerated mode. In TCG mode, it depends on the VCPU
> AA64MMFR0.PARANGE.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> v7 -> v8:
> - TCG PAMAX check moved in a separate patch
> 
> v6 -> v7
> - handle TCG case
> - set_memmap modifications moved to previous patches
> ---
>  hw/arm/virt.c | 21 +--------------------
>  1 file changed, 1 insertion(+), 20 deletions(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index a3da75a5ae..a45f0fcf79 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -95,21 +95,8 @@
>  
>  #define PLATFORM_BUS_NUM_IRQS 64
>  
> -/* RAM limit in GB. Since VIRT_MEM starts at the 1GB mark, this means
> - * RAM can go up to the 256GB mark, leaving 256GB of the physical
> - * address space unallocated and free for future use between 256G and 512G.
> - * If we need to provide more RAM to VMs in the future then we need to:
> - *  * allocate a second bank of RAM starting at 2TB and working up
> - *  * fix the DT and ACPI table generation code in QEMU to correctly
> - *    report two split lumps of RAM to the guest
> - *  * fix KVM in the host kernel to allow guests with >40 bit address spaces
> - * (We don't want to fill all the way up to 512GB with RAM because
> - * we might want it for non-RAM purposes later. Conversely it seems
> - * reasonable to assume that anybody configuring a VM with a quarter
> - * of a terabyte of RAM will be doing it on a host with more than a
> - * terabyte of physical address space.)
> - */
>  #define RAMBASE GiB
> +/* Legacy RAM limit in GB (< version 4.0) */
>  #define LEGACY_RAMLIMIT_GB 255
>  #define LEGACY_RAMLIMIT_BYTES (LEGACY_RAMLIMIT_GB * GiB)
do we need to keep these couple around?

it's used only in
 [VIRT_MEM] = { RAMBASE, LEGACY_RAMLIMIT_BYTES },
and doesn't have any effect whatsoever.
I'd set initial  VIRT_MEM.size to 0 and drop LEGACY_RAMLIMIT_*
maybe add comment above entry that size is defined by ram_size

>  
> @@ -1515,12 +1502,6 @@ static void machvirt_init(MachineState *machine)
>  
>      vms->smp_cpus = smp_cpus;
>  
> -    if (machine->ram_size > vms->memmap[VIRT_MEM].size) {
> -        error_report("mach-virt: cannot model more than %dGB RAM",
> -                     LEGACY_RAMLIMIT_GB);
> -        exit(1);
> -    }
> -
>      if (vms->virt && kvm_enabled()) {
>          error_report("mach-virt: KVM does not support providing "
>                       "Virtualization extensions to the guest CPU");