Re: [PATCH 5/6] KVM: PPC: Book3S Nested: Use explicit 4096 LPID maximum

[Fabiano Rosas <farosas@linux.ibm.com>]

Nicholas Piggin <npiggin@gmail.com> writes:

> Rather than tie this to KVMPPC_NR_LPIDS which is becoming more dynamic,
> fix it to 4096 (12-bits) explicitly for now.
>
> kvmhv_get_nested() does not have to check against KVM_MAX_NESTED_GUESTS
> because the L1 partition table registration hcall already did that, and
> it checks against the partition table size.
>
> This patch also puts all the partition table size calculations into the
> same form, using 12 for the architected size field shift and 4 for the
> shift corresponding to the partition table entry size.
>
> Signed-of-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

> ---
>  arch/powerpc/include/asm/kvm_host.h |  7 ++++++-
>  arch/powerpc/kvm/book3s_64_mmu_hv.c |  2 +-
>  arch/powerpc/kvm/book3s_hv_nested.c | 24 +++++++++++-------------
>  3 files changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 5fd0564e5c94..e6fb03884dcc 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -34,7 +34,12 @@
>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>  #include <asm/kvm_book3s_asm.h>		/* for MAX_SMT_THREADS */
>  #define KVM_MAX_VCPU_IDS	(MAX_SMT_THREADS * KVM_MAX_VCORES)
> -#define KVM_MAX_NESTED_GUESTS	KVMPPC_NR_LPIDS
> +
> +/*
> + * Limit the nested partition table to 4096 entries (because that's what
> + * hardware supports). Both guest and host use this value.
> + */
> +#define KVM_MAX_NESTED_GUESTS_SHIFT	12
>
>  #else
>  #define KVM_MAX_VCPU_IDS	KVM_MAX_VCPUS
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 5be92d5bc099..f983fb36cbf2 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -266,7 +266,7 @@ int kvmppc_mmu_hv_init(void)
>  			return -EINVAL;
>  		nr_lpids = 1UL << mmu_lpid_bits;
>  	} else {
> -		nr_lpids = KVM_MAX_NESTED_GUESTS;
> +		nr_lpids = 1UL << KVM_MAX_NESTED_GUESTS_SHIFT;
>  	}
>
>  	if (nr_lpids > KVMPPC_NR_LPIDS)
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index 1eff969b095c..75169e0753ce 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -439,10 +439,11 @@ long kvmhv_nested_init(void)
>  	if (!radix_enabled())
>  		return -ENODEV;
>
> -	/* find log base 2 of KVMPPC_NR_LPIDS, rounding up */
> -	ptb_order = __ilog2(KVMPPC_NR_LPIDS - 1) + 1;
> -	if (ptb_order < 8)
> -		ptb_order = 8;
> +	/* Partition table entry is 1<<4 bytes in size, hence the 4. */
> +	ptb_order = KVM_MAX_NESTED_GUESTS_SHIFT + 4;
> +	/* Minimum partition table size is 1<<12 bytes */
> +	if (ptb_order < 12)
> +		ptb_order = 12;
>  	pseries_partition_tb = kmalloc(sizeof(struct patb_entry) << ptb_order,
>  				       GFP_KERNEL);
>  	if (!pseries_partition_tb) {
> @@ -450,7 +451,7 @@ long kvmhv_nested_init(void)
>  		return -ENOMEM;
>  	}
>
> -	ptcr = __pa(pseries_partition_tb) | (ptb_order - 8);
> +	ptcr = __pa(pseries_partition_tb) | (ptb_order - 12);
>  	rc = plpar_hcall_norets(H_SET_PARTITION_TABLE, ptcr);
>  	if (rc != H_SUCCESS) {
>  		pr_err("kvm-hv: Parent hypervisor does not support nesting (rc=%ld)\n",
> @@ -534,16 +535,14 @@ long kvmhv_set_partition_table(struct kvm_vcpu *vcpu)
>  	long ret = H_SUCCESS;
>
>  	srcu_idx = srcu_read_lock(&kvm->srcu);
> -	/*
> -	 * Limit the partition table to 4096 entries (because that's what
> -	 * hardware supports), and check the base address.
> -	 */
> -	if ((ptcr & PRTS_MASK) > 12 - 8 ||
> +	/* Check partition size and base address. */
> +	if ((ptcr & PRTS_MASK) + 12 - 4 > KVM_MAX_NESTED_GUESTS_SHIFT ||
>  	    !kvm_is_visible_gfn(vcpu->kvm, (ptcr & PRTB_MASK) >> PAGE_SHIFT))
>  		ret = H_PARAMETER;
>  	srcu_read_unlock(&kvm->srcu, srcu_idx);
>  	if (ret == H_SUCCESS)
>  		kvm->arch.l1_ptcr = ptcr;
> +
>  	return ret;
>  }
>
> @@ -639,7 +638,7 @@ static void kvmhv_update_ptbl_cache(struct kvm_nested_guest *gp)
>
>  	ret = -EFAULT;
>  	ptbl_addr = (kvm->arch.l1_ptcr & PRTB_MASK) + (gp->l1_lpid << 4);
> -	if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 8))) {
> +	if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4))) {
>  		int srcu_idx = srcu_read_lock(&kvm->srcu);
>  		ret = kvm_read_guest(kvm, ptbl_addr,
>  				     &ptbl_entry, sizeof(ptbl_entry));
> @@ -809,8 +808,7 @@ struct kvm_nested_guest *kvmhv_get_nested(struct kvm *kvm, int l1_lpid,
>  {
>  	struct kvm_nested_guest *gp, *newgp;
>
> -	if (l1_lpid >= KVM_MAX_NESTED_GUESTS ||
> -	    l1_lpid >= (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4)))
> +	if (l1_lpid >= (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 12 - 4)))
>  		return NULL;
>
>  	spin_lock(&kvm->mmu_lock);