[PATCH 02/13] KVM: arm64: Clarify ESR_ELx_ERET_ISS_ERET*

[Joey Gouly]

On Tue, Feb 20, 2024 at 12:29:30PM +0000, Marc Zyngier wrote:
> On Tue, 20 Feb 2024 11:31:27 +0000,
> Joey Gouly <joey.gouly at arm.com> wrote:
> > 
> > On Mon, Feb 19, 2024 at 09:20:03AM +0000, Marc Zyngier wrote:
> > > The ESR_ELx_ERET_ISS_ERET* macros are a bit confusing:
> > > 
> > > - ESR_ELx_ERET_ISS_ERET really indicates that we have trapped an
> > >   ERETA* instruction, as opposed to an ERET
> > > 
> > > - ESR_ELx_ERET_ISS_ERETA reallu indicates that we have trapped
> > >   an ERETAB instruction, as opposed to an ERETAA.
> > > 
> > > Repaint the two helpers such as:
> > > 
> > > - ESR_ELx_ERET_ISS_ERET becomes ESR_ELx_ERET_ISS_ERETA
> > > 
> > > - ESR_ELx_ERET_ISS_ERETA becomes ESR_ELx_ERET_ISS_ERETAB
> > > 
> > > At the same time, use BIT() instead of raw values.
> > > 
> > > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > 
> > I'm somewhat against this, as the original names are what the Arm
> > ARM specifies.
> 
> I don't disagree, but that doesn't make the ARM ARM right! ;-)
> 
> > 
> > > ---
> > >  arch/arm64/include/asm/esr.h | 4 ++--
> > >  arch/arm64/kvm/handle_exit.c | 2 +-
> > >  2 files changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> > > index 353fe08546cf..72c7810ccf2c 100644
> > > --- a/arch/arm64/include/asm/esr.h
> > > +++ b/arch/arm64/include/asm/esr.h
> > > @@ -290,8 +290,8 @@
> > >  		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
> > >  
> > >  /* ISS field definitions for ERET/ERETAA/ERETAB trapping */
> > > -#define ESR_ELx_ERET_ISS_ERET		0x2
> > > -#define ESR_ELx_ERET_ISS_ERETA		0x1
> > > +#define ESR_ELx_ERET_ISS_ERETA		BIT(1)
> > > +#define ESR_ELx_ERET_ISS_ERETAB		BIT(0)
> > >  
> > >  /*
> > >   * ISS field definitions for floating-point exception traps
> > > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> > > index 617ae6dea5d5..0646c623d1da 100644
> > > --- a/arch/arm64/kvm/handle_exit.c
> > > +++ b/arch/arm64/kvm/handle_exit.c
> > > @@ -219,7 +219,7 @@ static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu)
> > >  
> > >  static int kvm_handle_eret(struct kvm_vcpu *vcpu)
> > >  {
> > > -	if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_ERET_ISS_ERET)
> > > +	if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_ERET_ISS_ERETA)
> > 
> > If this part is confusing due to the name, maybe introduce a function in esr.h
> > esr_is_pac_eret() (name pending bikeshedding)?
> 
> That's indeed a better option. Now for the bikeshed aspect:
> 
> - esr_iss_is_eretax(): check for ESR_ELx_ERET_ISS_ERET being set
> 
> - esr_iss_is_eretab(): check for ESR_ELx_ERET_ISS_ERETA being set
> 
> Thoughts?
> 

I was trying to avoid the ERETA* confusion by suggesting 'pac_eret', but if I
were to pick between your options I'd pick esr_iss_is_eretax().

Thanks,
Joey