linux-kernel - Re: [PATCH v5 05/10] KVM: arm/arm64: vgic-its: Save the collection table before device tables

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Date:   Wed, 25 Oct 2017 11:59:49 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, peter.maydell@...aro.org,
        andre.przywara@....com, wanghaibin.wang@...wei.com,
        wu.wubin@...wei.com, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH v5 05/10] KVM: arm/arm64: vgic-its: Save the collection
 table before device tables

On Mon, Oct 23, 2017 at 04:08:24PM +0200, Eric Auger wrote:
> Currently the ITS caches are not emptied on reset.
> 
> After a reset, in case we attempt to save the state before
> the bound devices have registered their MSIs and after the
> 1st level table has been allocated by the ITS driver
> (device BASER is valid), the first level entries are still
> invalid. If the device cache is not empty (devices registered
> before the reset), vgic_its_save_device_tables fails.
> 
> This failure has no consequence as those devices do not
> deserve to be saved: they correspond to the state before
> the reset.
> 
> However the ITS driver already sent MAPC for collections
> and those need to be saved. With the current code, they
> will not and the restored guest will not work properly.
> 
> So this patch saves collection tables  before device tables.
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> ---
> 
> candidate to be CC'ed stable
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index b6650c2..8472417 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2324,11 +2324,11 @@ static int vgic_its_save_tables_v0(struct vgic_its *its)
>  		return -EBUSY;
>  	}
>  
> -	ret = vgic_its_save_device_tables(its);
> +	ret = vgic_its_save_collection_table(its);
>  	if (ret)
>  		goto out;
>  
> -	ret = vgic_its_save_collection_table(its);
> +	ret = vgic_its_save_device_tables(its);
>  

I don't understand this.  It seems to indicate an ordering of device
tables vs. collection tables.  What is that?

I thought the point was that you'd want to save the valid table, and not
save the other one.

So, aren't we looking for something like this:

	ret = vgic_its_save_device_tables(its);
	if (ret < 0)
		goto out;
 
	ret = vgic_its_save_collection_table(its);


Thanks,
-Christoffer