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

From: Andrew Jones <[email-masked]>
Date: Mon, 13 Apr 2015 17:07:16 +0200

On Mon, Apr 13, 2015 at 03:51:33PM +0100, Alex Bennée wrote:
> 
> Christoffer Dall <[email-masked]> 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 <[email-masked]>
> >> 
> >> 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.

This change comes from a discussion we had on v1 of this series
http://www.spinics.net/lists/kvm-arm/msg12409.html

> 
> >
> >
> >> + */
> >> +#define __KVM_GUESTDBG_USE_SW_BP	(1 << 16)
> >> +#define __KVM_GUESTDBG_USE_HW_BP	(1 << 17)
> >> +
> >>  
> >>  struct kvm_guest_debug {
> >>  	__u32 control;
> >> -- 
> >> 2.3.4
> >> 
> 
> -- 
> Alex Bennée