Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752745AbbEZKAw (ORCPT ); Tue, 26 May 2015 06:00:52 -0400 Received: from www.linutronix.de ([62.245.132.108]:51242 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752270AbbEZKAv (ORCPT ); Tue, 26 May 2015 06:00:51 -0400 Date: Tue, 26 May 2015 12:00:26 +0200 (CEST) From: Thomas Gleixner To: "Wu, Feng" cc: "joro@8bytes.org" , "dwmw2@infradead.org" , "jiang.liu@linux.intel.com" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: RE: [v7 4/8] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts In-Reply-To: Message-ID: References: <1432531734-25978-1-git-send-email-feng.wu@intel.com> <1432531734-25978-5-git-send-email-feng.wu@intel.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1348 Lines: 38 On Tue, 26 May 2015, Wu, Feng wrote: > > On Mon, 25 May 2015, Feng Wu wrote: > > > + > > > + /* We don't need to modify irte if the interrupt is for posting. */ > > > + if (irte->pst != 1) > > > + modify_irte(&ir_data->irq_2_iommu, irte); > > > > I don't think this is correct. ir_data->irte_entry contains the non > > posted version, which has pst == 0. > > > > You need some other way to store whether you are in posted mode or > > not. > > Yes, seems this is incorrect. Thank you for pointing this out. After more > thinking about this, I think I can do it this way: > #1. Check the 'pst' field in hardware > #2. If 'pst' is 1, we don't update the IRTE in hardware. > > However, the question is the check and update operations should be protected > by the same spinlock ' irq_2_ir_lock ', otherwise, race condition may happen. Why? set_affinity() and vcpu_set_affinity() are serialized via irq_desc->lock. And vcpu_set_affinity() is the only way to switch from and to posted mode. So all you need is a field in intel_irq_data which captures whether posted is enabled or not. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/