Re: [PATCH 2/7] powerpc/watchpoint/kvm: Add infrastructure to support 2nd DAWR

[Paul Mackerras]

On Thu, Jul 23, 2020 at 03:50:53PM +0530, Ravi Bangoria wrote:
> kvm code assumes single DAWR everywhere. Add code to support 2nd DAWR.
> DAWR is a hypervisor resource and thus H_SET_MODE hcall is used to set/
> unset it. Introduce new case H_SET_MODE_RESOURCE_SET_DAWR1 for 2nd DAWR.

Is this the same interface as will be defined in PAPR and available
under PowerVM, or is it a new/different interface for KVM?

> Also, kvm will support 2nd DAWR only if CPU_FTR_DAWR1 is set.

In general QEMU wants to be able to control all aspects of the virtual
machine presented to the guest, meaning that just because a host has a
particular hardware capability does not mean we should automatically
present that capability to the guest.

In this case, QEMU will want a way to control whether the guest sees
the availability of the second DAWR/X registers or not, i.e. whether a
H_SET_MODE to set DAWR[X]1 will succeed or fail.

Paul.