Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756391AbaGPJCM (ORCPT ); Wed, 16 Jul 2014 05:02:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17043 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751980AbaGPJCH (ORCPT ); Wed, 16 Jul 2014 05:02:07 -0400 From: Vitaly Kuznetsov To: Konrad Rzeszutek Wilk Cc: stefano.stabellini@eu.citrix.com, xen-devel@lists.xenproject.org, Boris Ostrovsky , David Vrabel , Andrew Jones , linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 4/4] xen/pvhvm: Make MSI IRQs work after kexec References: <1405431640-649-1-git-send-email-vkuznets@redhat.com> <1405431640-649-5-git-send-email-vkuznets@redhat.com> <20140715152105.GP3403@laptop.dumpdata.com> Date: Wed, 16 Jul 2014 11:01:55 +0200 In-Reply-To: <20140715152105.GP3403@laptop.dumpdata.com> (Konrad Rzeszutek Wilk's message of "Tue, 15 Jul 2014 11:21:05 -0400") Message-ID: <87fvi1u16k.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Konrad Rzeszutek Wilk writes: > On Tue, Jul 15, 2014 at 03:40:40PM +0200, Vitaly Kuznetsov wrote: >> When kexec was peformed MSI IRQs for passthrough-ed devices were already >> mapped and we see non-zero pirq extracted from MSI msg. xen_irq_from_pirq() >> fails as we have no IRQ mapping information for that. Requesting for new >> mapping with __write_msi_msg() does not result in MSI IRQ being remapped so >> we don't recieve these IRQs. > > receive > Thanks for your comments! > How come '__write_msi_msg' does not result in new MSI IRQs? > Actually that was the hidden question in my RFC :-) Let me describe what I see. When normal boot is performed we have the following in xen_hvm_setup_msi_irqs(): __read_msi_msg() pirq -> 0 then we allocate new pirq with pirq = xen_allocate_pirq_msi() pirq -> 54 and we have the following mapping: xen: msi --> pirq=54 --> irq=72 in 'xl debug-keys i': (XEN) IRQ: 29 affinity:04 vec:b9 type=PCI-MSI status=00000030 in-flight=0 domain-list=7: 54(----), After kexec we see the following: __read_msi_msg() pirq -> 54 but as xen_irq_from_pirq() fails we follow the same path allocating new pirq: pirq = xen_allocate_pirq_msi() pirq -> 55 and we have the following mapping: xen: msi --> pirq=55 --> irq=75 However (afaict) mapping in xen wasn't updated: in 'xl debug-keys i': (XEN) IRQ: 29 affinity:02 vec:b9 type=PCI-MSI status=00000030 in-flight=0 domain-list=7: 54(--M-), > Is it fair to state that your code ends up reading the MSI IRQ (PIRQ) > from the device and updating the internal PIRQ<->IRQ code to match > with the reality? > Yea, 'always trust the device'. >> >> RFC: I wasn't able to understand why commit af42b8d1 which introduced >> xen_irq_from_pirq() check in xen_hvm_setup_msi_irqs() is checking that instead >> of checking pirq > 0 as if the mapping was already done (and we have pirq>0 here) >> we don't need to request for a new pirq. We're loosing existing PIRQ and I'm also >> not sure when __write_msi_msg() with new PIRQ will result in new mapping. > > We don't request a new pirq. We end up returning before we call xen_allocate_pirq_msi. > At least that is how the commit you mentioned worked. > I meant to say that in case we have pirq > 0 from __read_msi_msg() but xen_irq_from_pirq(pirq) fails (kexec-only case?) we always do xen_allocate_pirq_msi() which brings us new pirq. > In regards to why using 'xen_irq_from_pirq' instead of just checking the PIRQ - is > that we might be called twice by a buggy driver. As such we want to check > our PIRQ<->IRQ to figure this out. But if we're called twice we'll see the same pirq, right? Or there are some cases when we see 'crap' instead of pirq here? I think it would be nice to use the same pirq after kexec instead of allocating a new one even in case we can make remapping work. Thanks for your comments again! >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> arch/x86/pci/xen.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c >> index 905956f..685e8f1 100644 >> --- a/arch/x86/pci/xen.c >> +++ b/arch/x86/pci/xen.c >> @@ -231,8 +231,7 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, int nvec, int type) >> __read_msi_msg(msidesc, &msg); >> pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) | >> ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff); >> - if (msg.data != XEN_PIRQ_MSI_DATA || >> - xen_irq_from_pirq(pirq) < 0) { >> + if (msg.data != XEN_PIRQ_MSI_DATA || pirq <= 0) { >> pirq = xen_allocate_pirq_msi(dev, msidesc); >> if (pirq < 0) { >> irq = -ENODEV; >> -- >> 1.9.3 >> -- Vitaly -- 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/