On Mon, Oct 24 2022, Gavin Shan <gs...@redhat.com> wrote:
> After the improvement to high memory region address assignment is
> applied, the memory layout can be changed, introducing possible
> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
> is disabled or enabled when the optimization is applied or not, with
> the following configuration. The configuration is only achievable by
> modifying the source code until more properties are added to allow
> users selectively disable those high memory regions.
>
> pa_bits = 40;
> vms->highmem_redists = false;
> vms->highmem_ecam = false;
> vms->highmem_mmio = true;
>
> # qemu-system-aarch64 -accel kvm -cpu host \
> -machine virt-7.2,compact-highmem={on, off} \
> -m 4G,maxmem=511G -monitor stdio
>
> Region compact-highmem=off compact-highmem=on
> ----------------------------------------------------------------
> MEM [1GB 512GB] [1GB 512GB]
> HIGH_GIC_REDISTS2 [512GB 512GB+64MB] [disabled]
> HIGH_PCIE_ECAM [512GB+256MB 512GB+512MB] [disabled]
> HIGH_PCIE_MMIO [disabled] [512GB 1TB]
>
> In order to keep backwords compatibility, we need to disable the
> optimization on machine, which is virt-7.1 or ealier than it. It
> means the optimization is enabled by default from virt-7.2. Besides,
> 'compact-highmem' property is added so that the optimization can be
> explicitly enabled or disabled on all machine types by users.
>
> Signed-off-by: Gavin Shan <gs...@redhat.com>
> Reviewed-by: Cornelia Huck <coh...@redhat.com>
> Tested-by: Zhenyu Zhang <zheny...@redhat.com>
> ---
> docs/system/arm/virt.rst | 4 ++++
> hw/arm/virt.c | 32 ++++++++++++++++++++++++++++++++
> include/hw/arm/virt.h | 1 +
> 3 files changed, 37 insertions(+)
>
(...)
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 4896f600b4..11b5685432 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -174,6 +174,12 @@ static const MemMapEntry base_memmap[] = {
> * Note the extended_memmap is sized so that it eventually also includes the
> * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
> * index of base_memmap).
> + *
> + * The memory map for these Highmem IO Regions can be in legacy or compact
> + * layout, depending on 'compact-highmem' property. With legacy layout, the
> + * PA space for one specific region is always reserved, even the region has
s/even/even if/
> + * been disabled or doesn't fit into the PA space. However, the PA space for
> + * the region won't be reserved in these circumstances with compact layout.
> */
> static MemMapEntry extended_memmap[] = {
> /* Additional 64 MB redist region (can contain up to 512 redistributors)
> */
