linux-kernel - Re: [PATCH] tools/virtio: Test virtual address range detection

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Message-ID: <20220221170217.5bq7nhr3pvchku5x@sgarzare-redhat>
Date:   Mon, 21 Feb 2022 18:02:17 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools/virtio: Test virtual address range detection

On Mon, Feb 21, 2022 at 04:15:22PM +0000, David Woodhouse wrote:
>As things stand, an application which wants to use vhost with a trivial
>1:1 mapping of its virtual address space is forced to jump through hoops
>to detect what the address range might be. The VHOST_SET_MEM_TABLE ioctl
>helpfully doesn't fail immediately; you only get a failure *later* when
>you attempt to set the backend, if the table *could* map to an address
>which is out of range, even if no out-of-range address is actually
>being referenced.
>
>Since userspace is growing workarounds for this lovely kernel API, let's
>ensure that we have a regression test that does things basically the same
>way as https://gitlab.com/openconnect/openconnect/-/commit/443edd9d8826
>does.
>
>This is untested as I can't actually get virtio_test to work at all; it
>just seems to deadlock on a spinlock. But it's getting the right answer
>for the virtio range on x86_64 at least.

I had a similar issue with virtio_test and this simple patch [1] should 
fix the deadlock.

[1] 
https://lore.kernel.org/lkml/20220118150631.167015-1-sgarzare@redhat.com/

Stefano