Re: [PATCH] xen/arm: implement GICD_ICACTIVER read/write

[Julien Grall <julien.grall@citrix.com>]

Hi Stefano,

On 25/11/15 16:40, Stefano Stabellini wrote:
> Implement GICD_ICACTIVER and GICD_ISACTIVER reads by looking for the
> GIC_IRQ_GUEST_ACTIVE bit in the relevant struct pending_irq. However
> given that the pending to active transaction for irqs in LRs in done in
> hardware, the GIC_IRQ_GUEST_ACTIVE bit might be out of date. We'll have
> to live with that.

Looking to the Linux tree again, I found this commit:

commit 1c7d4dd46ee048afe19e1294634df6fa66862519
Author: Marc Zyngier <marc.zyngier@arm.com>
Date:   Mon Nov 16 19:13:28 2015 +0000

    irqchip/gic: Add save/restore of the active state

    When using EOImode==1, we may mark interrupts as being forwarded
    to a virtual machine. In that case, the interrupt is left active
    while being passed to the VM.

    If we suspend the system before the VM has deactivated the interrupt,
    the active state will be lost (which may be very annoying, as this
    may result in spurious interrupts and a confused guest).

    To avoid this, save and restore the active state together with the
    rest of the GIC registers.

    Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    Cc: <linux-arm-kernel@lists.infradead.org>
    Cc: Jason Cooper <jason@lakedaemon.net>
    Cc: Russell King <linux@arm.linux.org.uk>
    Link:
http://lkml.kernel.org/r/1447701208-18150-5-git-send-email-marc.zyngier@arm.com
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

So, we have to handle properly active/deactivate in order to get
suspend/resume working correctly.

Regards,

-- 
Julien Grall