Re: [PATCH 5/7] hw/virtio/virtio-mem: Convert VIRTIO_MEM_USABLE_EXTENT to runtime

["Alex Bennée" <alex.bennee@linaro.org>]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> Use qemu_arch_available() to check at runtime if a target
> architecture is built in.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  hw/virtio/virtio-mem.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index 5f57eccbb66..8c40042108c 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -15,6 +15,7 @@
>  #include "qemu/cutils.h"
>  #include "qemu/error-report.h"
>  #include "qemu/units.h"
> +#include "system/arch_init.h"
>  #include "system/numa.h"
>  #include "system/system.h"
>  #include "system/reset.h"
> @@ -170,13 +171,16 @@ static bool virtio_mem_has_shared_zeropage(RAMBlock *rb)
>   * necessary (as the section size can change). But it's more likely that the
>   * section size will rather get smaller and not bigger over time.
>   */
> -#if defined(TARGET_X86_64) || defined(TARGET_I386) || defined(TARGET_S390X)
> -#define VIRTIO_MEM_USABLE_EXTENT (2 * (128 * MiB))
> -#elif defined(TARGET_ARM)
> -#define VIRTIO_MEM_USABLE_EXTENT (2 * (512 * MiB))
> -#else
> -#error VIRTIO_MEM_USABLE_EXTENT not defined
> -#endif
> +static uint64_t virtio_mem_usable_extent_size(void)
> +{
> +    if (qemu_arch_available(QEMU_ARCH_I386 | QEMU_ARCH_S390X)) {
> +        return 2 * 128 * MiB;
> +    } else if (qemu_arch_available(QEMU_ARCH_ARM)) {
> +        return 2 * 512 * MiB;
> +    } else {
> +        g_assert_not_reached();
> +    }
> +}

What happens if/when we have multiple arches available? Won't we want to
know which CPU the virtio-mem device is attached to or do we take the
minimal value over the whole system?

>  
>  static bool virtio_mem_is_busy(void)
>  {
> @@ -721,7 +725,7 @@ static void virtio_mem_resize_usable_region(VirtIOMEM *vmem,
>                                              bool can_shrink)
>  {
>      uint64_t newsize = MIN(memory_region_size(&vmem->memdev->mr),
> -                           requested_size + VIRTIO_MEM_USABLE_EXTENT);
> +                           requested_size + virtio_mem_usable_extent_size());
>  
>      /* The usable region size always has to be multiples of the block size. */
>      newsize = QEMU_ALIGN_UP(newsize, vmem->block_size);

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro