Subject: Re: [PATCH v5 08/69] KVM: arm64: nv: Reset VCPU to EL2 registers if VCPU nested virt is set

From: Marc Zyngier <[email-masked]>
Date: Thu, 27 Jan 2022 12:43:43 +0000

On Mon, 17 Jan 2022 17:06:10 +0000,
"Russell King (Oracle)" <[email-masked]> wrote:
> 
> On Mon, Nov 29, 2021 at 08:00:49PM +0000, Marc Zyngier wrote:
> > From: Christoffer Dall <[email-masked]>
> > 
> > Reset the VCPU with PSTATE.M = EL2h when the nested virtualization
> > feature is enabled on the VCPU.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > [maz: rework register reset not to use empty data structures]
> > Signed-off-by: Marc Zyngier <[email-masked]>
> 
> Reviewed-by: Russell King (Oracle) <[email-masked]>
> 
> However, a couple of comments below.
> 
> > ---
> >  arch/arm64/kvm/reset.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> > index 426bd7fbc3fd..38a7182819fb 100644
> > --- a/arch/arm64/kvm/reset.c
> > +++ b/arch/arm64/kvm/reset.c
> > @@ -27,6 +27,7 @@
> >  #include <asm/kvm_asm.h>
> >  #include <asm/kvm_emulate.h>
> >  #include <asm/kvm_mmu.h>
> > +#include <asm/kvm_nested.h>
> >  #include <asm/virt.h>
> >  
> >  /* Maximum phys_shift supported for any VM on this host */
> > @@ -38,6 +39,9 @@ static u32 kvm_ipa_limit;
> >  #define VCPU_RESET_PSTATE_EL1	(PSR_MODE_EL1h | PSR_A_BIT | PSR_I_BIT | \
> >  				 PSR_F_BIT | PSR_D_BIT)
> >  
> > +#define VCPU_RESET_PSTATE_EL2	(PSR_MODE_EL2h | PSR_A_BIT | PSR_I_BIT | \
> > +				 PSR_F_BIT | PSR_D_BIT)
> > +
> >  #define VCPU_RESET_PSTATE_SVC	(PSR_AA32_MODE_SVC | PSR_AA32_A_BIT | \
> >  				 PSR_AA32_I_BIT | PSR_AA32_F_BIT)
> >  
> > @@ -176,8 +180,8 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> >  	if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit)
> >  		return false;
> >  
> > -	/* MTE is incompatible with AArch32 */
> > -	if (kvm_has_mte(vcpu->kvm) && is32bit)
> > +	/* MTE and NV are incompatible with AArch32 */
> > +	if ((kvm_has_mte(vcpu->kvm) || nested_virt_in_use(vcpu)) && is32bit)
> >  		return false;
> 
> It seems we have a bunch of:
> 
> 	if (something && is32bit)
> 		return false;
> 
> tests here - would it make sense to do:
> 
> 	if (is32bit) {
> 		if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
> 			return false;
> 
> 		/* MTE is incompatible with AArch32 */
> 		if (kvm_has_mte(vcpu->kvm))
> 			return false;
> 
> 		/* NV is incompatible with AArch32 */
> 		if (nested_virt_in_use(vcpu))
> 			return false;
> 	}
> 
> in terms of improved readability?

Agreed. I've now reworked to follow this pattern.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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