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

From: [email-masked] (Alex Bennée)
Date: Wed, 25 Jul 2018 16:41:44 +0100

Dave Martin <[email-masked]> writes:

> On Wed, Jul 25, 2018 at 03:12:15PM +0100, Alex Benn?e wrote:
>>
>> Dave Martin <[email-masked]> 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 <[email-masked]>
>> > ---
>> >  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).

It must be picked up elsewhere because it didn't fail when I rebuilt
without it - and the header has been happily using bool up to that
point.

> Cheers
> ---Dave

--
Alex Benn?e