Re: [PATCH v2 09/12] KVM: arm64: nv: Advertise support for FEAT_HPMN0

[Marc Zyngier <maz@kernel.org>]

On Tue, 27 Aug 2024 01:22:32 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> Everything is in place now for KVM to actually handle MDCR_EL2.HPMN. Not
> only that, the emulation is capable of doing FEAT_HPMN0. Advertise
> support for the feature in the VM's ID registers.
> 
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/arm64/kvm/nested.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index de789e0f1ae9..206aff3d88f7 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -910,12 +910,13 @@ static void limit_nv_id_regs(struct kvm *kvm)
>  				  ID_AA64MMFR4_EL1_E2H0_NI_NV1);
>  	kvm_set_vm_id_reg(kvm, SYS_ID_AA64MMFR4_EL1, val);
>  
> -	/* Only limited support for PMU, Debug, BPs and WPs */
> +	/* Only limited support for PMU, Debug, BPs, WPs, and HPMN0 */
>  	val = kvm_read_vm_id_reg(kvm, SYS_ID_AA64DFR0_EL1);
>  	val &= (NV_FTR(DFR0, PMUVer)	|
>  		NV_FTR(DFR0, WRPs)	|
>  		NV_FTR(DFR0, BRPs)	|
> -		NV_FTR(DFR0, DebugVer));
> +		NV_FTR(DFR0, DebugVer)	|
> +		NV_FTR(DFR0, HPMN0));

I don't think it does what you say it does! ;-)

What you probably want is something like

	val |= FIELD_PREP(NV_FTR(DFR0, HPMN0),
			  ID_AA64DFR0_EL1_HPMN0_DEF);

instead.

	M.

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