From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [v3 06/15] vmx: Extend struct pi_desc to support VT-d Posted-Interrupts Date: Wed, 15 Jul 2015 09:20:10 +0100 Message-ID: <55A633DA02000078000911AB@mail.emea.novell.com> 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: Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Feng Wu Cc: Kevin Tian , "keir@xen.org" , "george.dunlap@eu.citrix.com" , "andrew.cooper3@citrix.com" , "xen-devel@lists.xen.org" , Yang Z Zhang List-Id: xen-devel@lists.xenproject.org >>> On 15.07.15 at 04:40, wrote: > >> -----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. >> >> 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". >> > > When the vCPU is to be blocked, we need to atomically update > the "nv" and "ndst", then the wakeup notification event can be > delivered to the right destination. Okay. Your reply made me go through the patches again to check where updates to nv/ndst happen - what's the reason they aren't being updated as a pair in patch 14's RUNSTATE_running handling (or in the replacement draft's vmx_ctxt_switch_to() adjustment)? Jan