[Xen-devel] unhandled word causes Xen crash with recent Linux kernels, was: Re: [PATCH v2 05/11] xen/arm: vgic: Properly emulate the full register

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi Shannon,

On Wed, 25 Nov 2015, Shannon Zhao wrote:
> Upstream Linux kernel applies below patch which will write
> GICD_ICACTIVER. But since Xen doesn't support it, so it will cause Dom0
> initializes GIC failed.
> 
> 0eece2b22849c90b730815c893425a36b9d10fd5 (irqchip/gic: Make sure all
> interrupts are deactivated at boot)
> 
> (XEN) d0v0: vGICD: unhandled word write 0xffffffff to ICACTIVER4
> (XEN) traps.c:2447:d0v0 HSR=0x93860046 pc=0xffffffc0008d63f0
> gva=0xffffff8000004384 gpa=0x0000002f000384
> (XEN) DOM0: Unhandled fault: ttbr address size fault (0x96000000) at
> 0xffffff8000004384
> (XEN) DOM0: Internal error: : 96000000 [#1] PREEMPT SMP
> (XEN) DOM0: Modules linked in:
> (XEN) DOM0: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc2+ #364
> (XEN) DOM0: Hardware name: (null) (DT)
> (XEN) DOM0: task: ffffffc000969970 ti: ffffffc00095c000 task.ti:
> ffffffc00095c000
> (XEN) DOM0: PC is at gic_dist_config+0x78/0xa0
> (XEN) DOM0: LR is at __gic_init_bases+0x240/0x2bc
> 
> Do we have a plan to fix this?

Thanks for the reporting the issue, I can reproduce the problem.  Given
that this is a very serious regression and that we cannot really "fix"
the Linux side because Linux is not doing anything wrong, I think we
have to go with a very simple change, something we can easily backport
to all past Xen releases.

I suggest we turn the "unhandled word write" into a write_ignore, see
below:

---

xen/arm: ignore GICD_ICACTIVER writes

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff --git a/xen/arch/arm/vgic-v2.c b/xen/arch/arm/vgic-v2.c
index f7d784b..8585c44 100644
--- a/xen/arch/arm/vgic-v2.c
+++ b/xen/arch/arm/vgic-v2.c
@@ -332,11 +332,8 @@ static int vgic_v2_distr_mmio_write(struct vcpu *v, 
mmio_info_t *info,
         return 0;
 
     case GICD_ICACTIVER ... GICD_ICACTIVERN:
-        if ( dabt.size != DABT_WORD ) goto bad_width;
-        printk(XENLOG_G_ERR
-               "%pv: vGICD: unhandled word write %#"PRIregister" to 
ICACTIVER%d\n",
-               v, r, gicd_reg - GICD_ICACTIVER);
-        return 0;
+        /* we should really be implementing this */
+        goto write_ignore_32;
 
     case GICD_ITARGETSR ... GICD_ITARGETSR + 7:
         /* SGI/PPI target is read only */
diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
index b5249ff..6d77373 100644
--- a/xen/arch/arm/vgic-v3.c
+++ b/xen/arch/arm/vgic-v3.c
@@ -421,11 +421,8 @@ static int __vgic_v3_distr_common_mmio_write(const char 
*name, struct vcpu *v,
         return 0;
 
     case GICD_ICACTIVER ... GICD_ICACTIVERN:
-        if ( dabt.size != DABT_WORD ) goto bad_width;
-        printk(XENLOG_G_ERR
-               "%pv: %s: unhandled word write %#"PRIregister" to 
ICACTIVER%d\n",
-               v, name, r, reg - GICD_ICACTIVER);
-        return 0;
+        /* we should really be implementing this */
+        goto write_ignore_32;
 
     case GICD_IPRIORITYR ... GICD_IPRIORITYRN:
         if ( dabt.size != DABT_BYTE && dabt.size != DABT_WORD ) goto bad_width;

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