From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH] hvm/hpet: Correctly gate the virtual HPET on HVM_PARAM_HPET_ENABLE Date: Thu, 15 Jan 2015 15:49:03 +0000 Message-ID: <54B7E16F.2010609@citrix.com> References: <1421332842-28693-1-git-send-email-andrew.cooper3@citrix.com> <54B7EC2F02000078000557DF@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54B7EC2F02000078000557DF@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Tim Deegan , Keir Fraser , Xen-devel List-Id: xen-devel@lists.xenproject.org On 15/01/15 15:34, Jan Beulich wrote: >>>> On 15.01.15 at 15:40, wrote: >> c/s 3f8e22de7 "x86 hvm: Allow HPET to be configured as a per-domain config >> option" introduced the parameter to conditionally enable the HPET. >> >> However, having the check in hpet_range() does not have the intended effect. >> As currently implemented, when the HPET is disabled, the range is not >> claimed >> and an ioreq is forwarded to qemu, which implements an HPET itself. >> >> Properly disable the HPET by always claiming the range, dropping writes and >> reading ~0. > Hmm, while the patch certainly does what you describe above, is that > really correct? There could be something else at that address when > the HPET is disabled. Therefore I would rather think that qemu should > be told to also not make a HPET available when the option is off. Without out wiring up northbridge chipset reigsters from Qemu to Xen to control where components such as the HPET appear, I think we can reasonably assume that there will be nothing there. Whether the HPET is present or not, the range ought to reserved in the E820 and not free for arbitrary reuse by the OS. ~Andrew