Re: [PATCH v4 3/6] hw/arm/virt: Honor highmem setting when computing the memory map

[Eric Auger <eric.auger@redhat.com>]

Hi Marc,

On 1/7/22 5:33 PM, Marc Zyngier wrote:
> Even when the VM is configured with highmem=off, the highest_gpa
> field includes devices that are above the 4GiB limit.
> Similarily, nothing seem to check that the memory is within
> the limit set by the highmem=off option.
>
> This leads to failures in virt_kvm_type() on systems that have
> a crippled IPA range, as the reported IPA space is larger than
> what it should be.
>
> Instead, honor the user-specified limit to only use the devices
> at the lowest end of the spectrum, and fail if we have memory
> crossing the 4GiB limit.
>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric
> ---
>  hw/arm/virt.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 4d1d629432..57c55e8a37 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1663,7 +1663,7 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
>  static void virt_set_memmap(VirtMachineState *vms)
>  {
>      MachineState *ms = MACHINE(vms);
> -    hwaddr base, device_memory_base, device_memory_size;
> +    hwaddr base, device_memory_base, device_memory_size, memtop;
>      int i;
>  
>      vms->memmap = extended_memmap;
> @@ -1690,7 +1690,11 @@ static void virt_set_memmap(VirtMachineState *vms)
>      device_memory_size = ms->maxram_size - ms->ram_size + ms->ram_slots * GiB;
>  
>      /* Base address of the high IO region */
> -    base = device_memory_base + ROUND_UP(device_memory_size, GiB);
> +    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");
> +        exit(EXIT_FAILURE);
> +    }
>      if (base < device_memory_base) {
>          error_report("maxmem/slots too huge");
>          exit(EXIT_FAILURE);
> @@ -1707,7 +1711,7 @@ static void virt_set_memmap(VirtMachineState *vms)
>          vms->memmap[i].size = size;
>          base += size;
>      }
> -    vms->highest_gpa = base - 1;
> +    vms->highest_gpa = (vms->highmem ? base : memtop) - 1;
>      if (device_memory_size > 0) {
>          ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
>          ms->device_memory->base = device_memory_base;