Re: [Xen-devel] [PATCH 2/7] xen/arm/vgic-v2: Ignore write to GICD_ISACTIVERn registers

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 11 Apr 2018, Julien Grall wrote:
> On 11/04/18 14:19, 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. This should be fine for
> > now because reading these registers is already handled as 'read as zero'.
> 
> I think this patch is wrong. It is not mandatory for the guest to write
> exactly the same value as read. Assuming the guest will always write 0, then
> what you want to do is checking the write is actually 0. In that case you can
> ignore it. For all the other case, you should still fail.

Yes indeed, and that should be fine because GICD_ISACTIVER is already
implemented as read_as_zero.


> > 
> > Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
> > ---
> >   xen/arch/arm/vgic-v2.c | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/xen/arch/arm/vgic-v2.c b/xen/arch/arm/vgic-v2.c
> > index 646d1f3d12..b088376ed0 100644
> > --- a/xen/arch/arm/vgic-v2.c
> > +++ b/xen/arch/arm/vgic-v2.c
> > @@ -484,11 +484,10 @@ static int vgic_v2_distr_mmio_write(struct vcpu *v,
> > mmio_info_t *info,
> >           return 0;
> >         case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
> > -        if ( dabt.size != DABT_WORD ) goto bad_width;
> >           printk(XENLOG_G_ERR
> >                  "%pv: vGICD: unhandled word write %#"PRIregister" to
> > ISACTIVER%d\n",
> >                  v, r, gicd_reg - GICD_ISACTIVER);
> > -        return 0;
> > +        goto write_ignore_32;
> >         case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
> >           printk(XENLOG_G_ERR
> > 
> 
> -- 
> Julien Grall
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel