Re: [Xen-devel] [PATCH v2 02/10] xen/arm: Ignore write to GICD_ISACTIVERn registers (vgic-v2)

[Julien Grall <julien.grall@xxxxxxx>]

Hi Mirela,

On 20/04/18 13:25, Mirela Simonovic wrote:
> Guests attempt to write into these registers on resume (for example Linux).
> Without this patch a data abort exception will be raised to the guest.
> This patch handles the write access by ignoring it, but only if the value
> to be written is zero. This should be fine because reading these registers
> is already handled as 'read as zero'.
>
> Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
>
> ---
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> ---
> Changes in v2:
> - Write should be ignored only if the value to be written is zero
>   (in v1 the write was ignored regardless of the value)
> ---
>   xen/arch/arm/vgic-v2.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/vgic-v2.c b/xen/arch/arm/vgic-v2.c
> index 646d1f3d12..afd3e89883 100644
> --- a/xen/arch/arm/vgic-v2.c
> +++ b/xen/arch/arm/vgic-v2.c
> @@ -488,7 +488,9 @@ static int vgic_v2_distr_mmio_write(struct vcpu *v, 
> mmio_info_t *info,
>           printk(XENLOG_G_ERR
>                  "%pv: vGICD: unhandled word write %#"PRIregister" to 
> ISACTIVER%d\n",
>                  v, r, gicd_reg - GICD_ISACTIVER);
> -        return 0;
> +        if ( r != 0 )
> +            return 0;
It would be better to move the check before the printk. So a warning is 
avoided when the guest is writing 0.
Cheers,

> +        goto write_ignore_32;
>   
>       case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
>           printk(XENLOG_G_ERR
Cheers,

--
Julien Grall

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