Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

Hi Connie,

On 10/19/22 10:00 PM, Cornelia Huck wrote:
> On Wed, Oct 12 2022, Gavin Shan <gshan@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.
> >
> >    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
> >    ----------------------------------------------------------------
> >    RAM               [1GB         512GB]        [1GB         512GB]
> >    HIGH_GIC_REDISTS  [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 machines, 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 <gshan@redhat.com>
> > Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> > ---
> >   docs/system/arm/virt.rst |  4 ++++
> >   hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
> >   include/hw/arm/virt.h    |  1 +
> >   3 files changed, 52 insertions(+)
> >
> > diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> > index 20442ea2c1..75bf5a4994 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``.
> >   
> > +compact-highmem
> > +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
>
> Maybe s/compact space/the compact layout/ ?

Yeah, 'compact layout' is better. I will amend in next respin.

> > +  The default is ``on`` for machine types later than ``virt-7.2``
> > +
> >   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 c05cfb5314..8f1dba0ece 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -174,6 +174,27 @@ 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 addresses assigned to these regions are affected by 'compact-highmem'
> > + * property, which is to enable or disable the compact space in the Highmem
>
> s/space in/layout for/ ?

Agreed.

> > + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
> > + * depending on the property in the following scenario.
> > + *
> > + * 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
> > + * ----------------------------------------------------------------
> > + * RAM               [1GB         512GB]        [1GB         512GB]
> > + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
> > + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
> > + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
> >    */
> >   static MemMapEntry extended_memmap[] = {
> >       /* Additional 64 MB redist region (can contain up to 512 redistributors) 
> > */
>
> (...)
>
> > @@ -3124,8 +3167,12 @@ 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);
> > +    /* Compact space for high memory regions was introduced with 7.2 */
>
> s/space/layout/ ?

Ack.

> > +    vmc->no_highmem_compact = true;
> >   }
> >   DEFINE_VIRT_MACHINE(7, 1)
> >   
>
> Other than the wording nits, lgtm.
>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Thanks,
Gavin