Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-10-03 Thread Gavin Shan 

Hi Eric,

On 10/3/22 4:49 PM, Eric Auger wrote:

On 9/29/22 01:49, Gavin Shan wrote:

On 9/28/22 10:22 PM, Eric Auger wrote:

On 9/22/22 01:13, Gavin Shan wrote:

After the improvement to high memory region address assignment is
applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO

s/the memory layout is changed./the memory layout is changed,
introducing possible migration breakage.


Ok, much clearer.


memory region is enabled when the improvement is applied, but it's
disabled if the improvement isn't applied.

  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 -m 4G,maxmem=511G  \
    -monitor stdio

In order to keep backwords compatibility, we need to disable the
optimization on machines, which is virt-7.1 or ealier than it. It
means the optimization is enabled by default from virt-7.2. Besides,
'highmem-compact' property is added so that the optimization can be

I would rather rename the property into compact-highmem even if the vms
field is name highmem_compact to align with other highmem fields


Ok, but I would love to know why. Note that we already have
'highmem=on|off'. 'highmem_compact=on|off' seems consistent
to me.

To me the property name should rather sound 'english' with the adjective
before the name 'high memory"' but I am not a native english speaker
either.


Ok. I agree 'compact-highmem' is better. The backup variable name will
be still 'highmem_compact', which is consistent with the existing ones.




explicitly enabled or disabled on all machine types by users.

Signed-off-by: Gavin Shan 
---
   docs/system/arm/virt.rst |  4 
   hw/arm/virt.c    | 33 +
   include/hw/arm/virt.h    |  2 ++
   3 files changed, 39 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 20442ea2c1..f05ec2253b 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -94,6 +94,10 @@ highmem
     address space above 32 bits. The default is ``on`` for machine
types
     later than ``virt-2.12``.
   +highmem-compact
+  Set ``on``/``off`` to enable/disable compact space for high
memory regions.
+  The default is ``on`` for machine types later than ``virt-7.2``

I think you should document what is compact layout versus legacy one,
both in the commit msg and maybe as a comment in a code along with the
comment in hw/arm/virt.c starting with 'Highmem IO Regions: '


Ok, I will add this into the commit log in v4. I don't think it's
necessary
to add duplicate comment in the code. People can check the commit log for
details if needed.


+
   gic-version
     Specify the version of the Generic Interrupt Controller (GIC) to
provide.
     Valid values are:
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index b702f8f2b5..a4fbdaef91 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1734,6 +1734,13 @@ static void
virt_set_high_memmap(VirtMachineState *vms,
   base = region_base + region_size;
   } else {
   *region_enabled = false;
+
+    if (!vms->highmem_compact) {

this snippet should be already present in previous patch otherwise this
will break bisectability.



Hmm, nice catch! I think I need to swap PATCH[4] and PATCH[5] in next
revision. In that order, 'compact-highmem' is introduced in PATCH[4],
but not used yet. PATCH[5] has the optimization and 'compact-highmem'
is used.

No in general you introduce the property at the very end with the code
guarded with an unset vms->highmem_compact in the previous patch.



Yeah, what I need is define 'vms->highmem_compact' in PATCH[v3 4/5],
whose value is false. I also need to update @base and @vms->highest_gpa
on !vms->highmem_compact' in PATCH[v3 4/5].




+    base = region_base + region_size;
+    if (fits) {
+    vms->highest_gpa = region_base + region_size - 1;
+    }
+    }
   }
   }
   }
@@ -2348,6 +2355,20 @@ static void virt_set_highmem(Object *obj,
bool value, Error **errp)
   vms->highmem = value;
   }
   +static bool virt_get_highmem_compact(Object *obj, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    return vms->highmem_compact;
+}
+
+static void virt_set_highmem_compact(Object *obj, bool value, Error
**errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    vms->highmem_compact = value;
+}
+
   static bool virt_get_its(Object *obj, Error **errp)
   {
   VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -2966,6 +2987,13 @@ static void
virt_machine_class_init(ObjectClass *oc, void *data)
     "Set on/off to
enable/disable using "
     "physical address space
above 32 bits");
   +    object_class_property_add_bool(oc, "highmem-compact",
+ 

Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-10-03 Thread Eric Auger 
Hi Gavin,

On 9/29/22 01:49, Gavin Shan wrote:
> Hi Eric,
>
> On 9/28/22 10:22 PM, Eric Auger wrote:
>> On 9/22/22 01:13, Gavin Shan wrote:
>>> After the improvement to high memory region address assignment is
>>> applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO
>> s/the memory layout is changed./the memory layout is changed,
>> introducing possible migration breakage.
>
> Ok, much clearer.
>
>>> memory region is enabled when the improvement is applied, but it's
>>> disabled if the improvement isn't applied.
>>>
>>>  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 -m 4G,maxmem=511G  \
>>>    -monitor stdio
>>>
>>> In order to keep backwords compatibility, we need to disable the
>>> optimization on machines, which is virt-7.1 or ealier than it. It
>>> means the optimization is enabled by default from virt-7.2. Besides,
>>> 'highmem-compact' property is added so that the optimization can be
>> I would rather rename the property into compact-highmem even if the vms
>> field is name highmem_compact to align with other highmem fields
>
> Ok, but I would love to know why. Note that we already have
> 'highmem=on|off'. 'highmem_compact=on|off' seems consistent
> to me.
To me the property name should rather sound 'english' with the adjective
before the name 'high memory"' but I am not a native english speaker
either.
>
>>> explicitly enabled or disabled on all machine types by users.
>>>
>>> Signed-off-by: Gavin Shan 
>>> ---
>>>   docs/system/arm/virt.rst |  4 
>>>   hw/arm/virt.c    | 33 +
>>>   include/hw/arm/virt.h    |  2 ++
>>>   3 files changed, 39 insertions(+)
>>>
>>> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
>>> index 20442ea2c1..f05ec2253b 100644
>>> --- a/docs/system/arm/virt.rst
>>> +++ b/docs/system/arm/virt.rst
>>> @@ -94,6 +94,10 @@ highmem
>>>     address space above 32 bits. The default is ``on`` for machine
>>> types
>>>     later than ``virt-2.12``.
>>>   +highmem-compact
>>> +  Set ``on``/``off`` to enable/disable compact space for high
>>> memory regions.
>>> +  The default is ``on`` for machine types later than ``virt-7.2``
>> I think you should document what is compact layout versus legacy one,
>> both in the commit msg and maybe as a comment in a code along with the
>> comment in hw/arm/virt.c starting with 'Highmem IO Regions: '
>
> Ok, I will add this into the commit log in v4. I don't think it's
> necessary
> to add duplicate comment in the code. People can check the commit log for
> details if needed.
>
>>> +
>>>   gic-version
>>>     Specify the version of the Generic Interrupt Controller (GIC) to
>>> provide.
>>>     Valid values are:
>>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>>> index b702f8f2b5..a4fbdaef91 100644
>>> --- a/hw/arm/virt.c
>>> +++ b/hw/arm/virt.c
>>> @@ -1734,6 +1734,13 @@ static void
>>> virt_set_high_memmap(VirtMachineState *vms,
>>>   base = region_base + region_size;
>>>   } else {
>>>   *region_enabled = false;
>>> +
>>> +    if (!vms->highmem_compact) {
>> this snippet should be already present in previous patch otherwise this
>> will break bisectability.
>>
>
> Hmm, nice catch! I think I need to swap PATCH[4] and PATCH[5] in next
> revision. In that order, 'compact-highmem' is introduced in PATCH[4],
> but not used yet. PATCH[5] has the optimization and 'compact-highmem'
> is used.
No in general you introduce the property at the very end with the code
guarded with an unset vms->highmem_compact in the previous patch.

Thanks

Eric
>
>>> +    base = region_base + region_size;
>>> +    if (fits) {
>>> +    vms->highest_gpa = region_base + region_size - 1;
>>> +    }
>>> +    }
>>>   }
>>>   }
>>>   }
>>> @@ -2348,6 +2355,20 @@ static void virt_set_highmem(Object *obj,
>>> bool value, Error **errp)
>>>   vms->highmem = value;
>>>   }
>>>   +static bool virt_get_highmem_compact(Object *obj, Error **errp)
>>> +{
>>> +    VirtMachineState *vms = VIRT_MACHINE(obj);
>>> +
>>> +    return vms->highmem_compact;
>>> +}
>>> +
>>> +static void virt_set_highmem_compact(Object *obj, bool value, Error
>>> **errp)
>>> +{
>>> +    VirtMachineState *vms = VIRT_MACHINE(obj);
>>> +
>>> +    vms->highmem_compact = value;
>>> +}
>>> +
>>>   static bool virt_get_its(Object *obj, Error **errp)
>>>   {
>>>   VirtMachineState *vms = VIRT_MACHINE(obj);
>>> @@ -2966,6 +2987,13 @@ static void
>>> virt_machine_class_init(ObjectClass *oc, void *data)
>>>     "Set on/off to
>>> enable/disable using "
>>>     "physical address space
>>> above 32 bits");
>>>   +    object_class_property_add_bool(oc,

Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-09-29 Thread Gavin Shan 

Hi Cornelia,

On 9/29/22 8:27 PM, Cornelia Huck wrote:

On Thu, Sep 29 2022, Gavin Shan  wrote:

On 9/28/22 10:22 PM, Eric Auger wrote:

On 9/22/22 01:13, Gavin Shan wrote:

After the improvement to high memory region address assignment is
applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO

s/the memory layout is changed./the memory layout is changed,
introducing possible migration breakage.


Ok, much clearer.


memory region is enabled when the improvement is applied, but it's
disabled if the improvement isn't applied.

  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 -m 4G,maxmem=511G  \
-monitor stdio

In order to keep backwords compatibility, we need to disable the
optimization on machines, which is virt-7.1 or ealier than it. It
means the optimization is enabled by default from virt-7.2. Besides,
'highmem-compact' property is added so that the optimization can be

I would rather rename the property into compact-highmem even if the vms
field is name highmem_compact to align with other highmem fields


Ok, but I would love to know why. Note that we already have
'highmem=on|off'. 'highmem_compact=on|off' seems consistent
to me.


FWIW, I initially misread 'highmem_compact' as 'highmem_compat' (and had
to re-read because I got confused). At least to me, 'compact_highmem'
has less chance of being parsed incorrectly :) (although that is
probably a personal thing.)



Ok. 'compact-highmem' is also fine to me. I'm really bad at naming :)




explicitly enabled or disabled on all machine types by users.

Signed-off-by: Gavin Shan 
---
   docs/system/arm/virt.rst |  4 
   hw/arm/virt.c| 33 +
   include/hw/arm/virt.h|  2 ++
   3 files changed, 39 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 20442ea2c1..f05ec2253b 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -94,6 +94,10 @@ highmem
 address space above 32 bits. The default is ``on`` for machine types
 later than ``virt-2.12``.
   
+highmem-compact

+  Set ``on``/``off`` to enable/disable compact space for high memory regions.
+  The default is ``on`` for machine types later than ``virt-7.2``

I think you should document what is compact layout versus legacy one,
both in the commit msg and maybe as a comment in a code along with the
comment in hw/arm/virt.c starting with 'Highmem IO Regions: '


Ok, I will add this into the commit log in v4. I don't think it's necessary
to add duplicate comment in the code. People can check the commit log for
details if needed.


Rather explain it in this file here, maybe? I'd prefer to be able to
find out what 'compact' means without digging through the commit log.



Ok, lets do as Eric suggested. There are existing comments about
@extended_memmap[] in hw/arm/virt.c. We need to explain the legacy/modern
laoyout and 'compact-highmem' property there.

Thanks,
Gavin

Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-09-29 Thread Cornelia Huck 
On Thu, Sep 29 2022, Gavin Shan  wrote:

> Hi Eric,
>
> On 9/28/22 10:22 PM, Eric Auger wrote:
>> On 9/22/22 01:13, Gavin Shan wrote:
>>> After the improvement to high memory region address assignment is
>>> applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO
>> s/the memory layout is changed./the memory layout is changed,
>> introducing possible migration breakage.
>
> Ok, much clearer.
>
>>> memory region is enabled when the improvement is applied, but it's
>>> disabled if the improvement isn't applied.
>>>
>>>  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 -m 4G,maxmem=511G  \
>>>-monitor stdio
>>>
>>> In order to keep backwords compatibility, we need to disable the
>>> optimization on machines, which is virt-7.1 or ealier than it. It
>>> means the optimization is enabled by default from virt-7.2. Besides,
>>> 'highmem-compact' property is added so that the optimization can be
>> I would rather rename the property into compact-highmem even if the vms
>> field is name highmem_compact to align with other highmem fields
>
> Ok, but I would love to know why. Note that we already have
> 'highmem=on|off'. 'highmem_compact=on|off' seems consistent
> to me.

FWIW, I initially misread 'highmem_compact' as 'highmem_compat' (and had
to re-read because I got confused). At least to me, 'compact_highmem'
has less chance of being parsed incorrectly :) (although that is
probably a personal thing.)

>
>>> explicitly enabled or disabled on all machine types by users.
>>>
>>> Signed-off-by: Gavin Shan 
>>> ---
>>>   docs/system/arm/virt.rst |  4 
>>>   hw/arm/virt.c| 33 +
>>>   include/hw/arm/virt.h|  2 ++
>>>   3 files changed, 39 insertions(+)
>>>
>>> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
>>> index 20442ea2c1..f05ec2253b 100644
>>> --- a/docs/system/arm/virt.rst
>>> +++ b/docs/system/arm/virt.rst
>>> @@ -94,6 +94,10 @@ highmem
>>> address space above 32 bits. The default is ``on`` for machine types
>>> later than ``virt-2.12``.
>>>   
>>> +highmem-compact
>>> +  Set ``on``/``off`` to enable/disable compact space for high memory 
>>> regions.
>>> +  The default is ``on`` for machine types later than ``virt-7.2``
>> I think you should document what is compact layout versus legacy one,
>> both in the commit msg and maybe as a comment in a code along with the
>> comment in hw/arm/virt.c starting with 'Highmem IO Regions: '
>
> Ok, I will add this into the commit log in v4. I don't think it's necessary
> to add duplicate comment in the code. People can check the commit log for
> details if needed.

Rather explain it in this file here, maybe? I'd prefer to be able to
find out what 'compact' means without digging through the commit log.

Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-09-28 Thread Gavin Shan 

Hi Eric,

On 9/28/22 10:22 PM, Eric Auger wrote:

On 9/22/22 01:13, Gavin Shan wrote:

After the improvement to high memory region address assignment is
applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO

s/the memory layout is changed./the memory layout is changed,
introducing possible migration breakage.


Ok, much clearer.


memory region is enabled when the improvement is applied, but it's
disabled if the improvement isn't applied.

 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 -m 4G,maxmem=511G  \
   -monitor stdio

In order to keep backwords compatibility, we need to disable the
optimization on machines, which is virt-7.1 or ealier than it. It
means the optimization is enabled by default from virt-7.2. Besides,
'highmem-compact' property is added so that the optimization can be

I would rather rename the property into compact-highmem even if the vms
field is name highmem_compact to align with other highmem fields


Ok, but I would love to know why. Note that we already have
'highmem=on|off'. 'highmem_compact=on|off' seems consistent
to me.


explicitly enabled or disabled on all machine types by users.

Signed-off-by: Gavin Shan 
---
  docs/system/arm/virt.rst |  4 
  hw/arm/virt.c| 33 +
  include/hw/arm/virt.h|  2 ++
  3 files changed, 39 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 20442ea2c1..f05ec2253b 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -94,6 +94,10 @@ highmem
address space above 32 bits. The default is ``on`` for machine types
later than ``virt-2.12``.
  
+highmem-compact

+  Set ``on``/``off`` to enable/disable compact space for high memory regions.
+  The default is ``on`` for machine types later than ``virt-7.2``

I think you should document what is compact layout versus legacy one,
both in the commit msg and maybe as a comment in a code along with the
comment in hw/arm/virt.c starting with 'Highmem IO Regions: '


Ok, I will add this into the commit log in v4. I don't think it's necessary
to add duplicate comment in the code. People can check the commit log for
details if needed.


+
  gic-version
Specify the version of the Generic Interrupt Controller (GIC) to provide.
Valid values are:
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index b702f8f2b5..a4fbdaef91 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1734,6 +1734,13 @@ static void virt_set_high_memmap(VirtMachineState *vms,
  base = region_base + region_size;
  } else {
  *region_enabled = false;
+
+if (!vms->highmem_compact) {

this snippet should be already present in previous patch otherwise this
will break bisectability.



Hmm, nice catch! I think I need to swap PATCH[4] and PATCH[5] in next
revision. In that order, 'compact-highmem' is introduced in PATCH[4],
but not used yet. PATCH[5] has the optimization and 'compact-highmem'
is used.


+base = region_base + region_size;
+if (fits) {
+vms->highest_gpa = region_base + region_size - 1;
+}
+}
  }
  }
  }
@@ -2348,6 +2355,20 @@ static void virt_set_highmem(Object *obj, bool value, 
Error **errp)
  vms->highmem = value;
  }
  
+static bool virt_get_highmem_compact(Object *obj, Error **errp)

+{
+VirtMachineState *vms = VIRT_MACHINE(obj);
+
+return vms->highmem_compact;
+}
+
+static void virt_set_highmem_compact(Object *obj, bool value, Error **errp)
+{
+VirtMachineState *vms = VIRT_MACHINE(obj);
+
+vms->highmem_compact = value;
+}
+
  static bool virt_get_its(Object *obj, Error **errp)
  {
  VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -2966,6 +2987,13 @@ static void virt_machine_class_init(ObjectClass *oc, 
void *data)
"Set on/off to enable/disable using 
"
"physical address space above 32 
bits");
  
+object_class_property_add_bool(oc, "highmem-compact",

+   virt_get_highmem_compact,
+   virt_set_highmem_compact);
+object_class_property_set_description(oc, "highmem-compact",
+  "Set on/off to enable/disable compact 
"
+  "space for high memory regions");
+
  object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
virt_set_gic_version);
  object_class_property_set_description(oc, "gic-version",
@@ -3050,6 +3078,7 @@ static void virt_instance_init(Object *obj)
  
  /* High memory is enabled by default */

  vms->highmem = true;
+vms->highmem_compact = !vmc->no_highmem_compact;

Re: [PATCH v3 5/5] hw/arm/virt: Add 'highmem-compact' property

2022-09-28 Thread Eric Auger 
Hi Gavin,
On 9/22/22 01:13, Gavin Shan wrote:
> After the improvement to high memory region address assignment is
> applied, the memory layout is changed. For example, VIRT_HIGH_PCIE_MMIO
s/the memory layout is changed./the memory layout is changed,
introducing possible migration breakage.
> memory region is enabled when the improvement is applied, but it's
> disabled if the improvement isn't applied.
>
> 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 -m 4G,maxmem=511G  \
>   -monitor stdio
>
> In order to keep backwords compatibility, we need to disable the
> optimization on machines, which is virt-7.1 or ealier than it. It
> means the optimization is enabled by default from virt-7.2. Besides,
> 'highmem-compact' property is added so that the optimization can be
I would rather rename the property into compact-highmem even if the vms
field is name highmem_compact to align with other highmem fields
> explicitly enabled or disabled on all machine types by users.
>
> Signed-off-by: Gavin Shan 
> ---
>  docs/system/arm/virt.rst |  4 
>  hw/arm/virt.c| 33 +
>  include/hw/arm/virt.h|  2 ++
>  3 files changed, 39 insertions(+)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 20442ea2c1..f05ec2253b 100644
> --- a/docs/system/arm/virt.rst
> +++ b/docs/system/arm/virt.rst
> @@ -94,6 +94,10 @@ highmem
>address space above 32 bits. The default is ``on`` for machine types
>later than ``virt-2.12``.
>  
> +highmem-compact
> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
> +  The default is ``on`` for machine types later than ``virt-7.2``
I think you should document what is compact layout versus legacy one,
both in the commit msg and maybe as a comment in a code along with the
comment in hw/arm/virt.c starting with 'Highmem IO Regions: '
> +
>  gic-version
>Specify the version of the Generic Interrupt Controller (GIC) to provide.
>Valid values are:
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index b702f8f2b5..a4fbdaef91 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1734,6 +1734,13 @@ static void virt_set_high_memmap(VirtMachineState *vms,
>  base = region_base + region_size;
>  } else {
>  *region_enabled = false;
> +
> +if (!vms->highmem_compact) {
this snippet should be already present in previous patch otherwise this
will break bisectability.

> +base = region_base + region_size;
> +if (fits) {
> +vms->highest_gpa = region_base + region_size - 1;
> +}
> +}
>  }
>  }
>  }
> @@ -2348,6 +2355,20 @@ static void virt_set_highmem(Object *obj, bool value, 
> Error **errp)
>  vms->highmem = value;
>  }
>  
> +static bool virt_get_highmem_compact(Object *obj, Error **errp)
> +{
> +VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +return vms->highmem_compact;
> +}
> +
> +static void virt_set_highmem_compact(Object *obj, bool value, Error **errp)
> +{
> +VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +vms->highmem_compact = value;
> +}
> +
>  static bool virt_get_its(Object *obj, Error **errp)
>  {
>  VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -2966,6 +2987,13 @@ static void virt_machine_class_init(ObjectClass *oc, 
> void *data)
>"Set on/off to enable/disable 
> using "
>"physical address space above 32 
> bits");
>  
> +object_class_property_add_bool(oc, "highmem-compact",
> +   virt_get_highmem_compact,
> +   virt_set_highmem_compact);
> +object_class_property_set_description(oc, "highmem-compact",
> +  "Set on/off to enable/disable 
> compact "
> +  "space for high memory regions");
> +
>  object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
>virt_set_gic_version);
>  object_class_property_set_description(oc, "gic-version",
> @@ -3050,6 +3078,7 @@ static void virt_instance_init(Object *obj)
>  
>  /* High memory is enabled by default */
>  vms->highmem = true;
> +vms->highmem_compact = !vmc->no_highmem_compact;
>  vms->gic_version = VIRT_GIC_VERSION_NOSEL;
>  
>  vms->highmem_ecam = !vmc->no_highmem_ecam;
> @@ -3119,8 +3148,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>  
>  static void virt_machine_7_1_options(MachineClass *mc)
>  {
> +VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>  virt_machine_7_2_options(mc);
>  compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
> +/*