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Re: [qemu-s390x] [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O ha

From: Cornelia Huck
Subject: Re: [qemu-s390x] [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling
Date: Mon, 28 Jan 2019 18:13:55 +0100

On Fri, 25 Jan 2019 17:04:04 +0100
Halil Pasic <address@hidden> wrote:

> Do we expect userspace/QEMU to fence the bad scenarios as tries to do
> today, or is this supposed to change to hardware should sort out
> requests whenever possible.

Does my other mail answer that?

> The problem I see with the let the hardware sort it out is that, for that
> to work, we need to juggle multiple translations simultaneously (or am I
> wrong?). Doing that does not appear particularly simple to me.

None in the first stage, at most two in the second stage, I guess.

> Furthermore we would go through all that hassle knowingly that the sole
> reason is working around bugs. We still expect our Linux guests
> serializing it's ssch() stuff as it does today. Thus I would except this
> code not getting the love nor the coverage that would guard against bugs
> in that code.

So, we should have test code for that? (Any IBM-internal channel I/O
exercisers that may help?)

We should not rely on the guest being sane, although Linux probably is
in that respect.

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