linux-kernel - Re: [PATCH v1 5/5] KVM: s390: vsie: gmap_table

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Date:   Fri, 3 Apr 2020 15:03:04 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v1 5/5] KVM: s390: vsie: gmap_table_walk() simplifications

On 4/2/20 8:48 PM, David Hildenbrand wrote:
> Let's use asce_type where applicable. Also, simplify our sanity check for
> valid table levels and convert it into a WARN_ON_ONCE(). Check if we even
> have a valid gmap shadow as the very first step.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  arch/s390/mm/gmap.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index fd32ab566f57..3c801dae7988 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -790,17 +790,18 @@ static inline unsigned long *gmap_table_walk(struct gmap *gmap,
>  	const int asce_type = gmap->asce & _ASCE_TYPE_MASK;
>  	unsigned long *table;
>  
> -	if ((gmap->asce & _ASCE_TYPE_MASK) + 4 < (level * 4))
> -		return NULL;
>  	if (gmap_is_shadow(gmap) && gmap->removed)
>  		return NULL;
>  
> +	if (WARN_ON_ONCE(level > (asce_type >> 2) + 1))
> +		return NULL;
> +
>  	if (WARN_ON_ONCE(asce_type != _ASCE_TYPE_REGION1) &&
>  			 gaddr & (-1UL << (31 + (asce_type >> 2) * 11)))
>  		return NULL;
>  
>  	table = gmap->table;

We could also initialize this variable at the top, no?

> -	switch (gmap->asce & _ASCE_TYPE_MASK) {
> +	switch (asce_type) {
>  	case _ASCE_TYPE_REGION1:
>  		table += (gaddr & _REGION1_INDEX) >> _REGION1_SHIFT;
>  		if (level == 4)
> 




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