Re: [PATCH v4 3/8] x86/domain: allocate d->{iomem,irq}_caps before arch-specific initialization

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jul 31, 2025 at 07:21:54PM +0000, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> Move IRQ/IOMEM rangesets allocation before arch_domain_create().
> 
> That guarantees that arch-specific code could access those rangesets to
> register traps for emulation.
> 
> It is necessary for those emulators registering trap handlers and ensuring
> that emulated IRQs are not shared with the physical IRQs.
> 
> Move dom0_setup_permissions() call right after I/O rangesets are allocated.
> 
> Move pvh_setup_mmcfg() inside dom0_setup_permissions() close to the place
> where MMCFG ranges are initialized.

I'm a bit puzzled by this, you don't need I/O permission to setup
traps.  You can setup traps everywhere, the I/O rangesets control
whether a domain can access the physical resource, not whether
accesses can be emulated.

The dependency between MMCFG registration (pvh_setup_mmcfg()) and
calling dom0_setup_permissions() is because the later consumes the
MMCFG ranges added by the former to mark them as not accessible by
a PVH dom0.

I think you don't need this for vUARTS, as the ports are know at build
time, and hence you can block access to them without requiring the
actual vUART to be initialized.

Thanks, Roger.