Subject: Re: [PATCH kernel v2 1/6] KVM: PPC: Rework H_PUT_TCE/H_GET_TCE handlers

From: David Gibson <[email-masked]>
Date: Fri, 22 Jan 2016 11:42:45 +1100

On Thu, Jan 21, 2016 at 06:39:32PM +1100, Alexey Kardashevskiy wrote:
> This reworks the existing H_PUT_TCE/H_GET_TCE handlers to have following
> patches applied nicer.
> 
> This moves the ioba boundaries check to a helper and adds a check for
> least bits which have to be zeros.
> 
> The patch is pretty mechanical (only check for least ioba bits is added)
> so no change in behaviour is expected.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>

Concept looks good, but there are a couple of nits.

> ---
> Changelog:
> v2:
> * compare @ret with H_SUCCESS instead of assuming H_SUCCESS is zero
> * made error reporting cleaner
> ---
>  arch/powerpc/kvm/book3s_64_vio_hv.c | 111 +++++++++++++++++++++++-------------
>  1 file changed, 72 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index 89e96b3..862f9a2 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -35,71 +35,104 @@
>  #include <asm/ppc-opcode.h>
>  #include <asm/kvm_host.h>
>  #include <asm/udbg.h>
> +#include <asm/iommu.h>
>  
>  #define TCES_PER_PAGE	(PAGE_SIZE / sizeof(u64))
>  
> +/*
> + * Finds a TCE table descriptor by LIOBN.
> + *
> + * WARNING: This will be called in real or virtual mode on HV KVM and virtual
> + *          mode on PR KVM
> + */
> +static struct kvmppc_spapr_tce_table *kvmppc_find_table(struct kvm_vcpu *vcpu,
> +		unsigned long liobn)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvmppc_spapr_tce_table *stt;
> +
> +	list_for_each_entry_lockless(stt, &kvm->arch.spapr_tce_tables, list)

list_for_each_entry_lockless?  According to the comments in the
header, that's for RCU protected lists, whereas this one is just
protected by the lock in the kvm structure.  This is replacing a plain
list_for_each_entry().

> +		if (stt->liobn == liobn)
> +			return stt;
> +
> +	return NULL;
> +}
> +
> +/*
> + * Validates IO address.
> + *
> + * WARNING: This will be called in real-mode on HV KVM and virtual
> + *          mode on PR KVM
> + */
> +static long kvmppc_ioba_validate(struct kvmppc_spapr_tce_table *stt,
> +		unsigned long ioba, unsigned long npages)
> +{
> +	unsigned long mask = (1ULL << IOMMU_PAGE_SHIFT_4K) - 1;
> +	unsigned long idx = ioba >> IOMMU_PAGE_SHIFT_4K;
> +	unsigned long size = stt->window_size >> IOMMU_PAGE_SHIFT_4K;
> +
> +	if ((ioba & mask) || (idx + npages > size))

It doesn't matter for the current callers, but you should check for
overflow in idx + npages as well.

-- 
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