Re: [PATCH v8 09/11] i386/pc: bounds check phys-bits against max used GPA

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 15 Jul 2022 18:16:26 +0100
Joao Martins <joao.m.martins@oracle.com> wrote:

> Calculate max *used* GPA against the CPU maximum possible address
> and error out if the former surprasses the latter. This ensures
> max used GPA is reacheable by configured phys-bits. Default phys-bits
> on Qemu is TCG_PHYS_ADDR_BITS (40) which is enough for the CPU to
> address 1Tb (0xff ffff ffff) or 1010G (0xfc ffff ffff) in AMD hosts
> with IOMMU.
> 
> This is preparation for AMD guests with >1010G, where it will want relocate
> ram-above-4g to be after 1Tb instead of 4G.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>

Acked-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  hw/i386/pc.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index cda435e3baeb..f30661b7f1a2 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -880,6 +880,18 @@ static uint64_t pc_get_cxl_range_end(PCMachineState *pcms)
>      return start;
>  }
>  
> +static hwaddr pc_max_used_gpa(PCMachineState *pcms, uint64_t pci_hole64_size)
> +{
> +    X86CPU *cpu = X86_CPU(first_cpu);
> +
> +    /* 32-bit systems don't have hole64 thus return max CPU address */
> +    if (cpu->phys_bits <= 32) {
> +        return ((hwaddr)1 << cpu->phys_bits) - 1;
> +    }
> +
> +    return pc_pci_hole64_start() + pci_hole64_size - 1;
> +}
> +
>  void pc_memory_init(PCMachineState *pcms,
>                      MemoryRegion *system_memory,
>                      MemoryRegion *rom_memory,
> @@ -894,13 +906,28 @@ void pc_memory_init(PCMachineState *pcms,
>      MachineClass *mc = MACHINE_GET_CLASS(machine);
>      PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>      X86MachineState *x86ms = X86_MACHINE(pcms);
> +    hwaddr maxphysaddr, maxusedaddr;
>      hwaddr cxl_base, cxl_resv_end = 0;
> +    X86CPU *cpu = X86_CPU(first_cpu);
>  
>      assert(machine->ram_size == x86ms->below_4g_mem_size +
>                                  x86ms->above_4g_mem_size);
>  
>      linux_boot = (machine->kernel_filename != NULL);
>  
> +    /*
> +     * phys-bits is required to be appropriately configured
> +     * to make sure max used GPA is reachable.
> +     */
> +    maxusedaddr = pc_max_used_gpa(pcms, pci_hole64_size);
> +    maxphysaddr = ((hwaddr)1 << cpu->phys_bits) - 1;
> +    if (maxphysaddr < maxusedaddr) {
> +        error_report("Address space limit 0x%"PRIx64" < 0x%"PRIx64
> +                     " phys-bits too low (%u)",
> +                     maxphysaddr, maxusedaddr, cpu->phys_bits);
> +        exit(EXIT_FAILURE);
> +    }
> +
>      /*
>       * Split single memory region and use aliases to address portions of it,
>       * done for backwards compatibility with older qemus.