Re: [RFC PATCH 08/16] KVM: arm64: Support dynamically hideable system registers

Dave Martin
2018-07-25T14:36:20Z

On Wed, Jul 25, 2018 at 03:12:15PM +0100, Alex Bennée wrote:
>
> Dave Martin <Dave.Martin@arm.com> writes:
>
> > Some system registers may or may not logically exist for a vcpu
> > depending on whether certain architectural features are enabled for
> > the vcpu.
> >
> > In order to avoid spuriously emulating access to these registers
> > when they should not exist, or allowing the registers to be
> > spuriously enumerated or saved/restored through the ioctl
> > interface, a means is needed to allow registers to be hidden
> > depending on the vcpu configuration.
> >
> > In order to support this in a flexible way, this patch adds a
> > check_present() method to struct sys_reg_desc, and updates the
> > generic system register access and enumeration code to be aware of
> > it: if check_present() returns false, the code behaves as if the
> > register did not exist.
> >
> > For convenience, the complete check is wrapped up in a new helper
> > sys_reg_present().
> >
> > An attempt has been made to hook the new check into the generic
> > accessors for trapped system registers. This should reduce the
> > potential for future surprises, although the redundant check will
> > add a small cost. No system register depends on this functionality
> > yet, and some paths needing the check may also need attention.
> >
> > Naturally, this facility makes sense only for registers that are
> > trapped.
> >
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > ---
> > arch/arm64/kvm/sys_regs.c | 20 +++++++++++++++-----
> > arch/arm64/kvm/sys_regs.h | 11 +++++++++++
> > 2 files changed, 26 insertions(+), 5 deletions(-)

[...]

> > diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> > index cd710f8..dfbb342 100644
> > --- a/arch/arm64/kvm/sys_regs.h
> > +++ b/arch/arm64/kvm/sys_regs.h
> > @@ -22,6 +22,9 @@
> > #ifndef __ARM64_KVM_SYS_REGS_LOCAL_H__
> > #define __ARM64_KVM_SYS_REGS_LOCAL_H__
> >
> > +#include <linux/compiler.h>
> > +#include <linux/types.h>
>
> I can see why you want compiler.h, but why types.h?

For bool (though it felt a bit pedantic).

Cheers
---Dave