Re: [RFC PATCH 3/3] kvm: arm/arm64: vgic-its: fix return value for restore

[Christoffer Dall <cdall@linaro.org>]

Hi Eric,

On Wed, Sep 06, 2017 at 05:18:35PM +0200, Auger Eric wrote:
> Hi Wanghaibin,
> 
> On 06/09/2017 15:05, wanghaibin wrote:
> > This patch fix the migrate restore tables failure.
> > 
> > The same scene, at the destination, the restore tables interface traversal guest
> > memory, and check the dte/ite is valid or not.
> > If all dtes/ites are invalid, we will do try next one, and the last it will take
> > the 1 return value, but currently, it be treated as error. That's not correct.
> There's indeed a bug here! In case all entries are invalid we shouldn't
> return an error.
> 
> One solution could be to relax the error checking in scan_its_table()
> and do not return 1 when the whole length has been scanned. This would
> fix your issue.
> 
> drawback of that change:
> at the moment we check the consistency of the entry data (next offset
> field). At the moment if the next_offset points to an entry outside of
> the table scope we are able to return an error (for top level tables).
> 
> Otherwise, if we want to keep that check, I think we would need to add a
> bool *valid parameter to entry_fn_t. in scan_its_table() we would return
> 1 only if last fn() call returns valid and len <= 0.
> 

I don't really understand what you're proposing.

I think Wanghaibin's patch actually looks correct.  Is there any problem
with it that you see?

Thanks,
-Christoffer

> > 
> > This patch try to fix this problem.
> > 
> > Signed-off-by: wanghaibin <wanghaibin.wang@huawei.com>
> > ---
> >  virt/kvm/arm/vgic/vgic-its.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> > index 5c20352..2c69aeb 100644
> > --- a/virt/kvm/arm/vgic/vgic-its.c
> > +++ b/virt/kvm/arm/vgic/vgic-its.c
> > @@ -2025,7 +2025,7 @@ static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
> >  		return PTR_ERR(dev);
> >  
> >  	ret = vgic_its_restore_itt(its, dev);
> > -	if (ret) {
> > +	if (ret < 0) {
> >  		vgic_its_free_device(its->dev->kvm, dev);
> >  		return ret;
> >  	}
> > @@ -2147,9 +2147,6 @@ static int vgic_its_restore_device_tables(struct vgic_its *its)
> >  				     vgic_its_restore_dte, NULL);
> >  	}
> >  
> > -	if (ret > 0)
> > -		ret = -EINVAL;
> > -
> >  	return ret;
> >  }
> >  
> >