Re: [PATCH v2 02/10] KVM: define common __KVM_GUESTDBG_USE_SW/HW_BP values

Christoffer Dall
2015-04-14T08:24:48Z

On Mon, Apr 13, 2015 at 03:51:33PM +0100, Alex Bennée wrote:
>
> Christoffer Dall <christoffer.dall@linaro.org> writes:
>
> > On Tue, Mar 31, 2015 at 04:08:00PM +0100, Alex Bennée wrote:
> >> Currently x86, powerpc and soon arm64 use the same two architecture
> >> specific bits for guest debug support for software and hardware
> >> breakpoints. This makes the shared values explicit while leaving the
> >> gate open for another architecture to use some other value if they
> >> really really want to.
> >>
> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >>
> >> diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
> >> index ab4d473..1731569 100644
> >> --- a/arch/powerpc/include/uapi/asm/kvm.h
> >> +++ b/arch/powerpc/include/uapi/asm/kvm.h
> >> @@ -310,8 +310,8 @@ struct kvm_guest_debug_arch {
> >> * and upper 16 bits are architecture specific. Architecture specific defines
> >> * that ioctl is for setting hardware breakpoint or software breakpoint.
> >> */
> >> -#define KVM_GUESTDBG_USE_SW_BP 0x00010000
> >> -#define KVM_GUESTDBG_USE_HW_BP 0x00020000
> >> +#define KVM_GUESTDBG_USE_SW_BP __KVM_GUESTDBG_USE_SW_BP
> >> +#define KVM_GUESTDBG_USE_HW_BP __KVM_GUESTDBG_USE_HW_BP
> >>
> >> /* definition of registers in kvm_run */
> >> struct kvm_sync_regs {
> >> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> >> index d7dcef5..1438202 100644
> >> --- a/arch/x86/include/uapi/asm/kvm.h
> >> +++ b/arch/x86/include/uapi/asm/kvm.h
> >> @@ -250,8 +250,8 @@ struct kvm_debug_exit_arch {
> >> __u64 dr7;
> >> };
> >>
> >> -#define KVM_GUESTDBG_USE_SW_BP 0x00010000
> >> -#define KVM_GUESTDBG_USE_HW_BP 0x00020000
> >> +#define KVM_GUESTDBG_USE_SW_BP __KVM_GUESTDBG_USE_SW_BP
> >> +#define KVM_GUESTDBG_USE_HW_BP __KVM_GUESTDBG_USE_HW_BP
> >> #define KVM_GUESTDBG_INJECT_DB 0x00040000
> >> #define KVM_GUESTDBG_INJECT_BP 0x00080000
> >>
> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >> index 5eedf84..ce2db14 100644
> >> --- a/include/uapi/linux/kvm.h
> >> +++ b/include/uapi/linux/kvm.h
> >> @@ -525,8 +525,16 @@ struct kvm_s390_irq {
> >>
> >> /* for KVM_SET_GUEST_DEBUG */
> >>
> >> -#define KVM_GUESTDBG_ENABLE 0x00000001
> >> -#define KVM_GUESTDBG_SINGLESTEP 0x00000002
> >> +#define KVM_GUESTDBG_ENABLE (1 << 0)
> >> +#define KVM_GUESTDBG_SINGLESTEP (1 << 1)
> >> +
> >> +/*
> >> + * Architecture specific stuff uses the top 16 bits of the field,
> >
> > can you be more specific than 'stuff' here? features?
> >
> >> + * however there is some shared commonality for the common cases
> >
> > I don't like this sentence; shared commonality is a pleonasm and the use
> > of however makes it sounds like there's some caveat here.
>
> OK I can see that - after I looked it up ;-)
>
> > If the top 16 bits are indeed arhictecture specific, then I think they
> > should just be defined in their architecture specific headers. Unless
> > the idea here is that there's a fixed set of of flags that architectures
> > can choose to support, in which case it should simply be defined in the
> > common header.
>
> Well an architecture might not support some features and want to use
> those bits for something else? I didn't want to force the bottom two
> of the architecture specific bits to wasted if the features don't exist.
>
In that case I think the definition is local to each architecture and
should indeed just be duplicated. The __ definitions complicate more
than they help as they are exported to userspace etc. The KVM
maintainers may have a different view on this though.

-Christoffer