Re: Proposal for Porting Xen to Armv8-R64 - DraftA

[Julien Grall <julien@xxxxxxx>]

Hi Wei,

On 25/02/2022 10:48, Wei Chen wrote:
> > >     Armv8-R64 can support max to 256 MPU regions. But that's just
> > theoretical.
> > >     So we don't want to define `pr_t mpu_regions[256]`, this is a memory
> > waste
> > >     in most of time. So we decided to let the user specify through a
> > Kconfig
> > >     option. `CONFIG_ARM_MPU_EL1_PROTECTION_REGIONS` default value can be
> > `32`,
> > >     it's a typical implementation on Armv8-R64. Users will recompile Xen
> > when
> > >     their platform changes. So when the MPU changes, respecifying the
> > MPU
> > >     protection regions number will not cause additional problems.
> >
> > I wonder if we could probe the number of MPU regions at runtime and
> > dynamically allocate the memory needed to store them in arch_vcpu.
> We have considered to used a pr_t mpu_regions[0] in arch_vcpu. But it seems
> we will encounter some static allocated arch_vcpu problems and sizeof issue.
Does it need to be embedded in arch_vcpu? If not, then we could allocate 
memory outside and add a pointer in arch_vcpu.
Cheers,

--
Julien Grall