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Re: [Xen-devel] Xen hypervisor hangs on booting against c/s 16925

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Tue, 29 Jan 2008 10:54:10 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 29 Jan 2008 02:55:04 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AchiZUbahTjZkM5YEdyyYwAX8io7RQ==
  • Thread-topic: [Xen-devel] Xen hypervisor hangs on booting against c/s 16925

On 29/1/08 10:52, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> If we don't write to a MTRR WP region, then actually mapping as WC does not
>> matter. We never write to the range 0xc0000-0xfffff. Anything we write to
>> below 0xa0000 had better be RAM, or we've got bigger problems than the WP
>> attribute!
> Unfortunately it does matter - WC does not permit read caching, but
> does permit speculative reads. That's both not what we want.

Is your concern that something with read side effects (i.e., I/O) would be
mapped with WP type in the MTRR? Does that not seem rather unlikely?

Anyhow, WP attribute also allows read speculation, just like WC, so in
respect of read speculation it does not matter which caching attribute we
actually use.

 -- Keir

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