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Re: [Qemu-devel] [PATCH] Add a memory barrier to guest memory access fun

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] Add a memory barrier to guest memory access functions
Date: Mon, 21 May 2012 17:16:08 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1

Il 21/05/2012 14:18, Michael S. Tsirkin ha scritto:
>> > Almost all our
>> > devices were written without any thought given to ordering, so they
>> > basically can and should be considered as all broken.
> Problem is, a lot of code is likely broken even after you sprinkle
> barriers around. For example qemu might write A then B where guest driver
> expects to see B written before A.

This would be a bug in the guest driver, and usually relatively easy to
reproduce.  The specs (I know of UHCI) should be very precise on this
for obvious reasons.


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