Re: [PATCH v4 4/6] hw/arm/virt: Use the PA range to compute the memory map

[Eric Auger]

Hi Marc,

On 1/7/22 5:33 PM, Marc Zyngier wrote:
> The highmem attribute is nothing but another way to express the
> PA range of a VM. To support HW that has a smaller PA range then
> what QEMU assumes, pass this PA range to the virt_set_memmap()
> function, allowing it to correctly exclude highmem devices
> if they are outside of the PA range.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  hw/arm/virt.c | 53 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 46 insertions(+), 7 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 57c55e8a37..db4b0636e1 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1660,7 +1660,7 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState 
> *vms, int idx)
>      return arm_cpu_mp_affinity(idx, clustersz);
>  }
>  
> -static void virt_set_memmap(VirtMachineState *vms)
> +static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
>  {
>      MachineState *ms = MACHINE(vms);
>      hwaddr base, device_memory_base, device_memory_size, memtop;
> @@ -1678,6 +1678,13 @@ static void virt_set_memmap(VirtMachineState *vms)
>          exit(EXIT_FAILURE);
>      }
>  
> +    /*
> +     * !highmem is exactly the same as limiting the PA space to 32bit,
> +     * irrespective of the underlying capabilities of the HW.
> +     */
> +    if (!vms->highmem)
> +         pa_bits = 32;
you need {} according to the QEMU coding style. Welcome to a new shiny
world :-)
> +
>      /*
>       * We compute the base of the high IO region depending on the
>       * amount of initial and device memory. The device memory start/size
> @@ -1691,8 +1698,9 @@ static void virt_set_memmap(VirtMachineState *vms)
>  
>      /* Base address of the high IO region */
>      memtop = base = device_memory_base + ROUND_UP(device_memory_size, GiB);
> -    if (!vms->highmem && memtop > 4 * GiB) {
> -        error_report("highmem=off, but memory crosses the 4GiB limit\n");
> +    if (memtop > BIT_ULL(pa_bits)) {
> +         error_report("Addressing limited to %d bits, but memory exceeds it 
> by %llu bytes\n",
> +                      pa_bits, memtop - BIT_ULL(pa_bits));
>          exit(EXIT_FAILURE);
>      }
>      if (base < device_memory_base) {
> @@ -1711,7 +1719,13 @@ static void virt_set_memmap(VirtMachineState *vms)
>          vms->memmap[i].size = size;
>          base += size;
>      }
> -    vms->highest_gpa = (vms->highmem ? base : memtop) - 1;
> +
> +    /*
> +     * If base fits within pa_bits, all good. If it doesn't, limit it
> +     * to the end of RAM, which is guaranteed to fit within pa_bits.
> +     */
> +    vms->highest_gpa = (base <= BIT_ULL(pa_bits) ? base : memtop) - 1;
> +
>      if (device_memory_size > 0) {
>          ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
>          ms->device_memory->base = device_memory_base;
> @@ -1902,12 +1916,38 @@ static void machvirt_init(MachineState *machine)
>      unsigned int smp_cpus = machine->smp.cpus;
>      unsigned int max_cpus = machine->smp.max_cpus;
Move the cpu_type check before?

    if (!cpu_type_valid(machine->cpu_type)) {
        error_report("mach-virt: CPU type %s not supported",
machine->cpu_type);
        exit(1);
    }
>  
> +    possible_cpus = mc->possible_cpu_arch_ids(machine);
> +
>      /*
>       * In accelerated mode, the memory map is computed earlier in kvm_type()
>       * to create a VM with the right number of IPA bits.
>       */
>      if (!vms->memmap) {
> -        virt_set_memmap(vms);
> +        Object *cpuobj;
> +        ARMCPU *armcpu;
> +        int pa_bits;
> +
> +        /*
> +         * Instanciate a temporary CPU object to find out about what
> +         * we are about to deal with. Once this is done, get rid of
> +         * the object.
> +         */
> +        cpuobj = object_new(possible_cpus->cpus[0].type);
> +        armcpu = ARM_CPU(cpuobj);
> +
> +        if (object_property_get_bool(cpuobj, "aarch64", NULL)) {
> +            pa_bits = arm_pamax(armcpu);
> +        } else if (arm_feature(&armcpu->env, ARM_FEATURE_LPAE)) {
> +            /* v7 with LPAE */
> +            pa_bits = 40;
> +        } else {
> +            /* Anything else */
> +            pa_bits = 32;
> +        }
> +
> +        object_unref(cpuobj);
> +
> +        virt_set_memmap(vms, pa_bits);
>      }
>  
>      /* We can probe only here because during property set
> @@ -1989,7 +2029,6 @@ static void machvirt_init(MachineState *machine)
>  
>      create_fdt(vms);
>  
> -    possible_cpus = mc->possible_cpu_arch_ids(machine);
>      assert(possible_cpus->len == max_cpus);
>      for (n = 0; n < possible_cpus->len; n++) {
>          Object *cpuobj;
> @@ -2646,7 +2685,7 @@ static int virt_kvm_type(MachineState *ms, const char 
> *type_str)
>      max_vm_pa_size = kvm_arm_get_max_vm_ipa_size(ms, &fixed_ipa);
>  
>      /* we freeze the memory map to compute the highest gpa */
> -    virt_set_memmap(vms);
> +    virt_set_memmap(vms, max_vm_pa_size);
>  
>      requested_pa_size = 64 - clz64(vms->highest_gpa);
>  
Thanks

Eric