linux-kernel - Re: [PATCH v4 06/11] KVM: arm/arm64: vgic-its: Check GITS_CBASER validity before processing commands

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Date:   Wed, 18 Oct 2017 00:10:16 +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 v4 06/11] KVM: arm/arm64: vgic-its: Check GITS_CBASER
 validity before processing commands

On Tue, Oct 17, 2017 at 09:10:04AM +0200, Eric Auger wrote:
> At the moment vgic_its_process_commands() does not
> check the CBASER is valid before processing any command.
> Let's fix that.
> 
> Also rename cbaser local variable into cbaser_pa to avoid
> any confusion with the full register.
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 3b539d4..e18f1e4 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1301,17 +1301,20 @@ static void vgic_mmio_write_its_cbaser(struct kvm *kvm, struct vgic_its *its,
>  /* Must be called with the cmd_lock held. */
>  static void vgic_its_process_commands(struct kvm *kvm, struct vgic_its *its)
>  {
> -	gpa_t cbaser;
> +	gpa_t cbaser_pa;
>  	u64 cmd_buf[4];
>  
> -	/* Commands are only processed when the ITS is enabled. */
> -	if (!its->enabled)
> +	/*
> +	 * Commands are only processed when the ITS is enabled and
> +	 * CBASER is valid
> +	 */
> +	if (!its->enabled || (!(its->cbaser & GITS_CBASER_VALID)))

Is it valid to clear the CBASER valid bit after having enabled the ITS?
If not, I think you should check changes to CBASER and then this
shouldn't be necessary.



>  		return;
>  
> -	cbaser = CBASER_ADDRESS(its->cbaser);
> +	cbaser_pa = CBASER_ADDRESS(its->cbaser);
>  
>  	while (its->cwriter != its->creadr) {
> -		int ret = kvm_read_guest(kvm, cbaser + its->creadr,
> +		int ret = kvm_read_guest(kvm, cbaser_pa + its->creadr,
>  					 cmd_buf, ITS_CMD_SIZE);
>  		/*
>  		 * If kvm_read_guest() fails, this could be due to the guest
> -- 
> 2.5.5
> 

Otherwise, this looks fine.

Thanks,
-Christoffer