[PATCH v3 28/42] KVM: arm64: Use KVM-specific HCRX_EL2 RES0 mask

[Joey Gouly]

On Sat, Apr 26, 2025 at 01:28:22PM +0100, Marc Zyngier wrote:
> We do not have a computed table for HCRX_EL2, so statically define
> the bits we know about. A warning will fire if the architecture
> grows bits that are not handled yet.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Reviewed-by: Joey Gouly <joey.gouly at arm.com>

> ---
>  arch/arm64/include/asm/kvm_arm.h | 18 ++++++++++++++----
>  arch/arm64/kvm/emulate-nested.c  |  5 +++++
>  arch/arm64/kvm/nested.c          |  4 ++--
>  3 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index e7c73d16cd451..52b3aeb19efc6 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -315,10 +315,20 @@
>  				 GENMASK(19, 18) |	\
>  				 GENMASK(15, 0))
>  
> -/* Polarity masks for HCRX_EL2 */
> -#define __HCRX_EL2_RES0         HCRX_EL2_RES0
> -#define __HCRX_EL2_MASK		(BIT(6))
> -#define __HCRX_EL2_nMASK	~(__HCRX_EL2_RES0 | __HCRX_EL2_MASK)
> +/*
> + * Polarity masks for HCRX_EL2, limited to the bits that we know about
> + * at this point in time. It doesn't mean that we actually *handle*
> + * them, but that at least those that are not advertised to a guest
> + * will be RES0 for that guest.
> + */
> +#define __HCRX_EL2_MASK		(BIT_ULL(6))
> +#define __HCRX_EL2_nMASK	(GENMASK_ULL(24, 14) | \
> +				 GENMASK_ULL(11, 7)  | \
> +				 GENMASK_ULL(5, 0))
> +#define __HCRX_EL2_RES0		~(__HCRX_EL2_nMASK | __HCRX_EL2_MASK)
> +#define __HCRX_EL2_RES1		~(__HCRX_EL2_nMASK | \
> +				  __HCRX_EL2_MASK  | \
> +				  __HCRX_EL2_RES0)

Convoluted way of writing 0, but it makes sense!

>  
>  /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
>  #define HPFAR_MASK	(~UL(0xf))
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index c30d970bf81cb..c581cf29bc59e 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -2157,6 +2157,7 @@ int __init populate_nv_trap_config(void)
>  	BUILD_BUG_ON(__NR_CGT_GROUP_IDS__ > BIT(TC_CGT_BITS));
>  	BUILD_BUG_ON(__NR_FGT_GROUP_IDS__ > BIT(TC_FGT_BITS));
>  	BUILD_BUG_ON(__NR_FG_FILTER_IDS__ > BIT(TC_FGF_BITS));
> +	BUILD_BUG_ON(__HCRX_EL2_MASK & __HCRX_EL2_nMASK);
>  
>  	for (int i = 0; i < ARRAY_SIZE(encoding_to_cgt); i++) {
>  		const struct encoding_to_trap_config *cgt = &encoding_to_cgt[i];
> @@ -2182,6 +2183,10 @@ int __init populate_nv_trap_config(void)
>  		}
>  	}
>  
> +	if (__HCRX_EL2_RES0 != HCRX_EL2_RES0)
> +		kvm_info("Sanitised HCR_EL2_RES0 = %016llx, expecting %016llx\n",
> +			 __HCRX_EL2_RES0, HCRX_EL2_RES0);
> +
>  	kvm_info("nv: %ld coarse grained trap handlers\n",
>  		 ARRAY_SIZE(encoding_to_cgt));
>  
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 479ffd25eea63..666df85230c9b 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -1058,8 +1058,8 @@ int kvm_init_nv_sysregs(struct kvm_vcpu *vcpu)
>  	set_sysreg_masks(kvm, HCR_EL2, res0, res1);
>  
>  	/* HCRX_EL2 */
> -	res0 = HCRX_EL2_RES0;
> -	res1 = HCRX_EL2_RES1;
> +	res0 = __HCRX_EL2_RES0;
> +	res1 = __HCRX_EL2_RES1;
>  	if (!kvm_has_feat(kvm, ID_AA64ISAR3_EL1, PACM, TRIVIAL_IMP))
>  		res0 |= HCRX_EL2_PACMEn;
>  	if (!kvm_has_feat(kvm, ID_AA64PFR2_EL1, FPMR, IMP))
> -- 
> 2.39.2
>