[PATCH v8 09/69] KVM: arm64: nv: Reset VMPIDR_EL2 and VPIDR_EL2 to sane values

[Oliver Upton]

On Tue, Jan 31, 2023 at 10:04:40PM +0000, Marc Zyngier wrote:
> On Tue, 31 Jan 2023 20:17:50 +0000, Oliver Upton <oliver.upton at linux.dev> wrote:
> > 
> > On Tue, Jan 31, 2023 at 09:24:04AM +0000, Marc Zyngier wrote:
> > > From: Christoffer Dall <christoffer.dall at arm.com>
> > > 
> > > The VMPIDR_EL2 and VPIDR_EL2 are architecturally UNKNOWN at reset, but
> > > let's be nice to a guest hypervisor behaving foolishly and reset these
> > > to something reasonable anyway.
> > 
> > Must we be so kind? :)
> > 
> > In all seriousness, I've found the hexspeak value of reset_unknown() to
> > be a rather useful debugging aid. And I can promise you that I'll use NV
> > to debug my own crap changes!
> > 
> > Any particular reason against just using reset_unknown()?
> 
> Because debugging NV itself is hell when all you have is a model!

Blech!

> As we were trying to debug the early code base, we really wanted to
> make it easy to run tiny guests without much setup, and work out of
> the box. That's how this sort of changes came about.
> 
> In any case, something like this the hack below works as well (I just
> booted an L1 and a couple of L2s with it, and nothing caught fire).

LGTM, mind squashing it into the previous patch?

-- 
Thanks,
Oliver

> 	M.
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 924afc40ab8b..c1016a35a996 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -924,16 +924,6 @@ static void reset_mpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>  	vcpu_write_sys_reg(vcpu, compute_reset_mpidr(vcpu), MPIDR_EL1);
>  }
>  
> -static void reset_vmpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> -{
> -	vcpu_write_sys_reg(vcpu, compute_reset_mpidr(vcpu), VMPIDR_EL2);
> -}
> -
> -static void reset_vpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> -{
> -	vcpu_write_sys_reg(vcpu, read_cpuid_id(), VPIDR_EL2);
> -}
> -
>  static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
>  				   const struct sys_reg_desc *r)
>  {
> @@ -2678,8 +2668,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	{ PMU_SYS_REG(SYS_PMCCFILTR_EL0), .access = access_pmu_evtyper,
>  	  .reset = reset_val, .reg = PMCCFILTR_EL0, .val = 0 },
>  
> -	EL2_REG(VPIDR_EL2, access_rw, reset_vpidr, 0),
> -	EL2_REG(VMPIDR_EL2, access_rw, reset_vmpidr, 0),
> +	EL2_REG(VPIDR_EL2, access_rw, reset_unknown, 0),
> +	EL2_REG(VMPIDR_EL2, access_rw, reset_unknown, 0),
>  	EL2_REG(SCTLR_EL2, access_rw, reset_val, SCTLR_EL2_RES1),
>  	EL2_REG(ACTLR_EL2, access_rw, reset_val, 0),
>  	EL2_REG(HCR_EL2, access_rw, reset_val, 0),
> 
> -- 
> Without deviation from the norm, progress is not possible.