linux-kernel - Re: [PATCH v3 07/12] KVM: arm/arm64: Adapt vgic_v3_check

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Message-ID: <557b2aaf-3f6f-ea11-55e2-5667b651922b@redhat.com>
Date:   Thu, 26 Apr 2018 10:29:35 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoffer Dall <christoffer.dall@....com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, cdall@...nel.org, peter.maydell@...aro.org,
        andre.przywara@....com, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH v3 07/12] KVM: arm/arm64: Adapt vgic_v3_check_base to
 multiple rdist regions

Hi Christoffer,
On 04/24/2018 11:07 PM, Christoffer Dall wrote:
> On Fri, Apr 13, 2018 at 10:20:53AM +0200, Eric Auger wrote:
>> We introduce a new helper to check there is no overlap between
>> dist region (if set) and registered rdist regions. This both
>> handles the case of legacy single rdist region (implicitly sized
>> with the number of online vcpus) and the new case of multiple
>> explicitly sized rdist regions.
> 
> I don't understand this change, really.  Is this just a cleanup, or
> changing some functionality (why?).
> 
> I think this could have come with the introduction of
> vgic_v3_rdist_overlap() before patch 6, and then patch 6 could have been
> simplified (hopefully) to just call this "check that nothing in the
> world ever collides withi itself" function.
I have merged this patch and vgic_v3_rd_region_size +
vgic_v3_rdist_overlap and put it before this patch.

Also I reworked the commit message which was unclear I acknowledge.

With respect to using the adapted  vgic_v3_check_base() in
vgic_v3_insert_redist_region(), it is less obvious to me.

In vgic_v3_insert_redist_region we do the checks *before* inserting the
new rdist region in the list of redist regions. While
vgic_v3_check_base() does the checks on already registered rdist and
dist regions. So I would be tempted to leave
vgic_v3_insert_redist_region() implementation as it is.

Thanks

Eric
> 
>>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>> ---
>>  virt/kvm/arm/vgic/vgic-v3.c | 26 +++++++++-----------------
>>  1 file changed, 9 insertions(+), 17 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>> index dbcba5f..b80f650 100644
>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>> @@ -432,31 +432,23 @@ bool vgic_v3_rdist_overlap(struct kvm *kvm, gpa_t base, size_t size)
>>  bool vgic_v3_check_base(struct kvm *kvm)
>>  {
>>  	struct vgic_dist *d = &kvm->arch.vgic;
>> -	gpa_t redist_size = KVM_VGIC_V3_REDIST_SIZE;
>> -	struct vgic_redist_region *rdreg =
>> -		list_first_entry(&d->rd_regions,
>> -				 struct vgic_redist_region, list);
>> -
>> -	redist_size *= atomic_read(&kvm->online_vcpus);
>> +	struct vgic_redist_region *rdreg;
>>  
>>  	if (!IS_VGIC_ADDR_UNDEF(d->vgic_dist_base) &&
>>  	    d->vgic_dist_base + KVM_VGIC_V3_DIST_SIZE < d->vgic_dist_base)
>>  		return false;
>>  
>> -	if (rdreg && (rdreg->base + redist_size < rdreg->base))
>> -		return false;
>> +	list_for_each_entry(rdreg, &d->rd_regions, list) {
>> +		if (rdreg->base + vgic_v3_rd_region_size(kvm, rdreg) <
>> +			rdreg->base)
>> +			return false;
>> +	}
>>  
>> -	/* Both base addresses must be set to check if they overlap */
>> -	if (IS_VGIC_ADDR_UNDEF(d->vgic_dist_base) || !rdreg)
>> +	if (IS_VGIC_ADDR_UNDEF(d->vgic_dist_base))
>>  		return true;
>>  
>> -	if (d->vgic_dist_base + KVM_VGIC_V3_DIST_SIZE <= rdreg->base)
>> -		return true;
>> -
>> -	if (rdreg->base + redist_size <= d->vgic_dist_base)
>> -		return true;
>> -
>> -	return false;
>> +	return !vgic_v3_rdist_overlap(kvm, d->vgic_dist_base,
>> +				      KVM_VGIC_V3_DIST_SIZE);
>>  }
>>  
>>  /**
>> -- 
>> 2.5.5
>>
> Otherwise this patch looks correct to me.
> 
> Thanks,
> -Christoffer
>