Re: [PATCH] KVM: PPC: Book3S HV: Disable HPT resizing on POWER9 for now

[David Gibson <david@gibson.dropbear.id.au>]

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On Sat, Feb 18, 2017 at 08:41:40AM +1100, Paul Mackerras wrote:
> The new HPT resizing code added in commit b5baa6877315 ("KVM: PPC:
> Book3S HV: KVM-HV HPT resizing implementation", 2016-12-20) doesn't
> have code to handle the new HPTE format which POWER9 uses.  Thus it
> would be best not to advertise it to userspace on POWER9 systems
> until it works properly.
> 
> Also, since resize_hpt_rehash_hpte() contains BUG_ON() calls that
> could be hit on POWER9, let's prevent it from being called on POWER9
> for now.
> 
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Acked-by: David Gibson <david@gibson.dropbear.id.au>

I probably would have put the check on entry to the prepare path,
rather than deep in the rehashing, but we need the fix one way or
another.

> ---
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 6 ++++++
>  arch/powerpc/kvm/powerpc.c          | 3 ++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index b68b342..f3158fb 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -1370,6 +1370,12 @@ static int resize_hpt_rehash(struct kvm_resize_hpt *resize)
>  	unsigned  long i;
>  	int rc;
>  
> +	/*
> +	 * resize_hpt_rehash_hpte() doesn't handle the new-format HPTEs
> +	 * that POWER9 uses, and could well hit a BUG_ON on POWER9.
> +	 */
> +	if (cpu_has_feature(CPU_FTR_ARCH_300))
> +		return -EIO;
>  	for (i = 0; i < kvmppc_hpt_npte(&kvm->arch.hpt); i++) {
>  		rc = resize_hpt_rehash_hpte(resize, i);
>  		if (rc != 0)
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 2b3e4e6..fcb253b 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -613,7 +613,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		r = 1;
>  		break;
>  	case KVM_CAP_SPAPR_RESIZE_HPT:
> -		r = !!hv_enabled;
> +		/* Disable this on POWER9 until code handles new HPTE format */
> +		r = !!hv_enabled && !cpu_has_feature(CPU_FTR_ARCH_300);
>  		break;
>  #endif
>  	case KVM_CAP_PPC_HTM:

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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