From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Wu, Feng" Subject: Re: [v3 06/15] vmx: Extend struct pi_desc to support VT-d Posted-Interrupts Date: Wed, 15 Jul 2015 03:13:05 +0000 Message-ID: References: <1435123109-10481-1-git-send-email-feng.wu@intel.com> <1435123109-10481-7-git-send-email-feng.wu@intel.com> <559FDFD4020000780008F85F@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <559FDFD4020000780008F85F@mail.emea.novell.com> Content-Language: en-US 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: "Tian, Kevin" , "keir@xen.org" , "george.dunlap@eu.citrix.com" , "andrew.cooper3@citrix.com" , "xen-devel@lists.xen.org" , "Zhang, Yang Z" , "Wu, Feng" List-Id: xen-devel@lists.xenproject.org > -----Original Message----- > From: Jan Beulich [mailto:JBeulich@suse.com] > Sent: Friday, July 10, 2015 9:08 PM > To: Wu, Feng > Cc: andrew.cooper3@citrix.com; george.dunlap@eu.citrix.com; Tian, Kevin; > Zhang, Yang Z; xen-devel@lists.xen.org; keir@xen.org > Subject: Re: [v3 06/15] vmx: Extend struct pi_desc to support VT-d > Posted-Interrupts > > >>> On 24.06.15 at 07:18, wrote: > > @@ -81,8 +81,19 @@ struct vmx_domain { > > > > struct pi_desc { > > DECLARE_BITMAP(pir, NR_VECTORS); > > - u32 control; > > - u32 rsvd[7]; > > + union { > > + struct > > + { > > + u16 on : 1, /* bit 256 - Outstanding Notification */ > > + sn : 1, /* bit 257 - Suppress Notification */ > > + rsvd_1 : 14; /* bit 271:258 - Reserved */ > > + u8 nv; /* bit 279:272 - Notification Vector */ > > + u8 rsvd_2; /* bit 287:280 - Reserved */ > > + u32 ndst; /* bit 319:288 - Notification Destination */ > > + }; > > + u64 control; > > + }; > > So current code, afaics, uses e.g. test_and_set_bit() to set ON. > By also declaring this as a bitfield you're opening the structure for > non-atomic accesses. If that's correct, why is other code not > being changed to _only_ use the bitfield mechanism (likely also > eliminating the need for it being a union with the now 64-bit > "control"? If atomic accesses are required, then I'd strongly > suggest against making this a bit field. All this fields are defined in the hardware Spec, if we define nv, ndst, but not define on and sn explicitly, it is a little strange. But you are right, I should use the same type to access them, e.g, bitfield mechanism. Thanks, Feng > > And in no event can I see why "ndst" needs to be union-ized > with "control" if it doesn't need to be updated atomically with > e.g. "nv". > > Jan