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From: Markus Armbruster <armbru@redhat.com>
References: <20171110173421.17904-1-lprosek@redhat.com>
	<20171110173421.17904-2-lprosek@redhat.com>
Date: Mon, 13 Nov 2017 15:22:40 +0100
In-Reply-To: <20171110173421.17904-2-lprosek@redhat.com> (Ladi Prosek's
	message of "Fri, 10 Nov 2017 18:34:19 +0100")
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Subject: Re: [Qemu-devel] [PATCH 1/3] ivshmem: Don't update non-existent MSI
 routes
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To: Ladi Prosek <lprosek@redhat.com>
Cc: qemu-devel@nongnu.org, geoff@hostfission.com, pbonzini@redhat.com, marcandre.lureau@redhat.com

Ladi Prosek <lprosek@redhat.com> writes:

> As of commit 660c97eef6f8 ("ivshmem: use kvm irqfd for msi notifications"),
> QEMU crashes with:
>
>   kvm_irqchip_commit_routes: Assertion `ret == 0' failed.
>
> if the ivshmem device is configured with more vectors than what the server
> supports. This is caused by the ivshmem_vector_unmask() being called on
> vectors that have not been initialized by ivshmem_add_kvm_msi_virq().
>
> This commit fixes it by adding a simple check to the mask and unmask
> callbacks.
>
> Note that the opposite mismatch, if the server supplies more vectors than
> what the device is configured for, is already handled and leads to output
> like:
>
>   Too many eventfd received, device has 1 vectors
>
> Fixes: 660c97eef6f8 ("ivshmem: use kvm irqfd for msi notifications")
> Signed-off-by: Ladi Prosek <lprosek@redhat.com>

I think I understand your description of what's wrong.  Not obvious to
me is how it can happen.  The cover letter mentions a Windows ivshmem
driver.  Is this a device bug a driver can trigger?  If yes, how?