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


From: Gavin Shan
Subject: Re: [PATCH v4 5/6] hw/arm/virt: Improve high memory region address
Date: Wed, 5 Oct 2022 06:58:28 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0

Hi Connie,

On 10/4/22 6:53 PM, Cornelia Huck wrote:
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?)


It looks overkill to me since the code is simple and clear. However,
comments won't be harmful. I will integrate the proposed comment
in next respin.

Thanks,
Gavin






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