linux-kernel - Re: [PATCH v2 05/10] KVM: arm/arm64: vgic-its: Check GITS_CBASER validity before processing commands

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Message-ID: <44a357a8-6ef2-4fd3-597d-3efd28317056@arm.com>
Date:   Fri, 6 Oct 2017 15:38:29 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Eric Auger <eric.auger@...hat.com>, eric.auger.pro@...il.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        marc.zyngier@....com, cdall@...aro.org, peter.maydell@...aro.org,
        wanghaibin.wang@...wei.com
Cc:     wu.wubin@...wei.com
Subject: Re: [PATCH v2 05/10] KVM: arm/arm64: vgic-its: Check GITS_CBASER
 validity before processing commands

Hi,

On 27/09/17 14:28, 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.

Good catch, but actually it goes a bit further:

"When GITS_CTLR.Enabled is written from 0 to 1 behavior is UNPREDICTABLE
if any of the following conditions are true:
· GITS_CBASER.Valid == 0.
...
"

So I think we need to check it upon setting CTLR.Enabled.
I did this in Xen, but forgot to fix this in KVM as well:
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/arm/vgic-v3-its.c;hb=HEAD#l1164

Cheers,
Andre.

> 
> 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 60ecf91..720552c 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)))
>  		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
>