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Re: [PATCH v4 5/6] hw/arm/virt: Improve high memory region address


From: Cornelia Huck
Subject: Re: [PATCH v4 5/6] hw/arm/virt: Improve high memory region address
Date: Tue, 04 Oct 2022 12:53:48 +0200
User-agent: Notmuch/0.37 (https://notmuchmail.org)

On Tue, Oct 04 2022, Gavin Shan <gshan@redhat.com> wrote:

> There are three high memory regions, which are VIRT_HIGH_REDIST2,
> VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
> are floating on highest RAM address. However, they can be disabled
> in several cases.
>
> (1) One specific high memory region is disabled by developer by
>     toggling vms->highmem_{redists, ecam, mmio}.
>
> (2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
>     'virt-2.12' or ealier than it.
>
> (3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
>     on 32-bits system.
>
> (4) One specific high memory region is disabled when it breaks the
>     PA space limit.
>
> The current implementation of virt_set_memmap() isn't comprehensive
> because the space for one specific high memory region is always
> reserved from the PA space for case (1), (2) and (3). In the code,
> 'base' and 'vms->highest_gpa' are always increased for those three
> cases. It's unnecessary since the assigned space of the disabled
> high memory region won't be used afterwards.
>
> This improves the address assignment for those three high memory
> region by skipping the address assignment for one specific high
> memory region if it has been disabled in case (1), (2) and (3).
> 'vms->high_compact' is false for now, meaning that we don't have
> any behavior changes until it becomes configurable through property
> 'compact-highmem' in next patch.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  hw/arm/virt.c         | 19 ++++++++++++-------
>  include/hw/arm/virt.h |  1 +
>  2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 59de7b78b5..4164da49e9 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1715,9 +1715,6 @@ static void virt_set_high_memmap(VirtMachineState *vms,
>          region_base = ROUND_UP(base, extended_memmap[i].size);
>          region_size = extended_memmap[i].size;
>  
> -        vms->memmap[i].base = region_base;
> -        vms->memmap[i].size = region_size;
> -
>          /*
>           * Check each device to see if they fit in the PA space,
>           * moving highest_gpa as we go.

Maybe tweak this comment?

"Check each enabled device to see if they fit in the PA space,
moving highest_gpa as we go. For compatibility, move highest_gpa
for disabled fitting devices as well, if the compact layout has
been disabled."

(Or would that be overkill?)




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