From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B720C432BE for ; Sat, 21 Aug 2021 22:14:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F1B3B61266 for ; Sat, 21 Aug 2021 22:14:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230397AbhHUWP3 (ORCPT ); Sat, 21 Aug 2021 18:15:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229927AbhHUWP2 (ORCPT ); Sat, 21 Aug 2021 18:15:28 -0400 Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37865C061575; Sat, 21 Aug 2021 15:14:48 -0700 (PDT) Received: by mail-ej1-x62c.google.com with SMTP id z20so27901813ejf.5; Sat, 21 Aug 2021 15:14:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=N+hik/cixapObGzvFN3C9sH7wClAUqIJeKpPSLmVoBQ=; b=g786+7deKKXxJtWM7wcVUu4v6958rQ5EjAmBnJ3NIkySKlPwdph3omEhxNyH0/6GL2 FXOYD/ehgvFo/rWkbfvKer0hXq9KHo+Y2N6cUAHNkUSYQRwAy30bVDoJdwc8zDMvr93/ 8uduxu80OFzS0Y2Rj2/Ky4A92j/2GqGX9Ga13KtkkW/H1+XTuCsSwboJaJk+Q6VKuq/5 0qOiMm9Ewsx22vyZHDUMtGztJ+CQPX/H7Nmjkuwp3ukYVizYFkR3C9thbUzT19K8DVal qzsK8zkBZvWJMwBZQwUzGEsbhZS9TBXL8u1coEC+ReIwZmaQN2UBm8KjTsan9KvKgkEo epmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=N+hik/cixapObGzvFN3C9sH7wClAUqIJeKpPSLmVoBQ=; b=Lg8KmQgiQR8XS3JlbuvMMe/DqrMzPdT67cdaDIO1Q1ft6AQxLDeHxOYJdNxWw6tR2k vwYvOMsmsvPphoDM1pCNNP+MPqZPSdZ2V2Z5cVCA6S9SXwPuUqVfVRVuw5QNLnh2ywDs fZatOCyFUAg9OoF20smF9GEJucjnBgcIBeujSwfBjGmbIgnnAGS7PaDOZrru0W4B8SIr E9YlWlXc0Ff6T+yvpthnQXvSSiDMkJNiM/YWrQbXHLHo5llLW1+YvOE/GtBHG5IPFZsG O+DqZkucRMVFwaIqBZ0C0FLdS3nm5nd1JZ+rNqf2jmBo3Cs911+jTrP+YAO20nU3Sfyr aBQg== X-Gm-Message-State: AOAM532pRBfLH4XDD5lyRXZqkASFcbx128SsJ+ycpSLMfnt3wYsO16xW rQa/Crgm7Fxg7RXmdDmK+b7Ml/qXB756wil5mRI= X-Google-Smtp-Source: ABdhPJyXzgDdct8CSp+cu+YTlhvKOMoO7iYD+n8tbrK5ykiqSnfloquu0yzVz5vhtDp0UOyqjJxGBzbY9o7khmhpJRg= X-Received: by 2002:a17:906:11c7:: with SMTP id o7mr28425576eja.480.1629584086740; Sat, 21 Aug 2021 15:14:46 -0700 (PDT) MIME-Version: 1.0 References: <20210820223744.8439-2-21cnbao@gmail.com> <20210820233328.GA3368938@bjorn-Precision-5520> <877dgfqdsg.wl-maz@kernel.org> In-Reply-To: <877dgfqdsg.wl-maz@kernel.org> From: Barry Song <21cnbao@gmail.com> Date: Sun, 22 Aug 2021 10:14:35 +1200 Message-ID: Subject: Re: [PATCH v2 1/2] PCI/MSI: Fix the confusing IRQ sysfs ABI for MSI-X To: Marc Zyngier Cc: Bjorn Helgaas , Bjorn Helgaas , Jonathan Corbet , Jonathan.Cameron@huawei.com, bilbao@vt.edu, Greg Kroah-Hartman , leon@kernel.org, LKML , linux-pci@vger.kernel.org, Linuxarm , luzmaximilian@gmail.com, mchehab+huawei@kernel.org, schnelle@linux.ibm.com, Barry Song , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 21, 2021 at 10:42 PM Marc Zyngier wrote: > > Hi Bjorn, > > On Sat, 21 Aug 2021 00:33:28 +0100, > Bjorn Helgaas wrote: > > > > [+cc Thomas, Marc] > > > > On Sat, Aug 21, 2021 at 10:37:43AM +1200, Barry Song wrote: > > > From: Barry Song > > > > > > /sys/bus/pci/devices/.../irq sysfs ABI is very confusing at this > > > moment especially for MSI-X cases. > > > > AFAICT this patch *only* affects MSI-X. So are you saying the sysfs > > ABI is fine for MSI but confusing for MSI-X? > > > > > While MSI sets IRQ to the first > > > number in the vector, MSI-X does nothing for this though it saves > > > default_irq in msix_setup_entries(). Weird the saved default_irq > > > for MSI-X is never used in pci_msix_shutdown(), which is quite > > > different with pci_msi_shutdown(). Thus, this patch moves to show > > > the first IRQ number which is from the first msi_entry for MSI-X. > > > Hopefully, this can make IRQ ABI more clear and more consistent. > > > > > > Acked-by: Greg Kroah-Hartman > > > Signed-off-by: Barry Song > > > --- > > > drivers/pci/msi.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c > > > index 9232255..6bbf81b 100644 > > > --- a/drivers/pci/msi.c > > > +++ b/drivers/pci/msi.c > > > @@ -771,6 +771,7 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries, > > > int ret; > > > u16 control; > > > void __iomem *base; > > > + struct msi_desc *desc; > > > > > > /* Ensure MSI-X is disabled while it is set up */ > > > pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0); > > > @@ -814,6 +815,10 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries, > > > pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_MASKALL, 0); > > > > > > pcibios_free_irq(dev); > > > + > > > + desc = first_pci_msi_entry(dev); > > > + dev->irq = desc->irq; > > > > This change is not primarily about sysfs. This is about changing > > "dev->irq" when MSI-X is enabled, and it's only incidental that sysfs > > reflects that. > > > > So we need to know the effect of changing dev->irq. Drivers may use > > the value of dev->irq, and I'm *guessing* this change shouldn't break > > them since we already do this for MSI, but I'd like some more expert > > opinion than mine :) > > > > For MSI we have: > > > > msi_capability_init > > msi_setup_entry > > entry = alloc_msi_entry(nvec) > > entry->msi_attrib.default_irq = dev->irq; /* Save IOAPIC IRQ */ > > dev->irq = entry->irq; > > > > pci_msi_shutdown > > /* Restore dev->irq to its default pin-assertion IRQ */ > > dev->irq = desc->msi_attrib.default_irq; > > > > and for MSI-X we have: > > > > msix_capability_init > > msix_setup_entries > > for (i = 0; i < nvec; i++) > > entry = alloc_msi_entry(1) > > entry->msi_attrib.default_irq = dev->irq; > > > > pci_msix_shutdown > > for_each_pci_msi_entry(entry, dev) > > __pci_msix_desc_mask_irq > > + dev->irq = entry->msi_attrib.default_irq; # added by this patch > > > > > > Things that seem strange to me: > > > > - The msi_setup_entry() comment "Save IOAPIC IRQ" seems needlessly > > specific; maybe it should be "INTx IRQ". > > > > - The pci_msi_shutdown() comment "Restore ... pin-assertion IRQ" > > should match the msi_setup_entry() one, e.g., maybe it should also > > be "INTx IRQ". There are no INTx or IOAPIC pins in PCIe. > > > > - The only use of .default_irq is to save and restore dev->irq, so > > it looks like a per-device thing, not a per-vector thing. > > > > In msi_setup_entry() there's only one msi_entry, so there's only > > one saved .default_irq. > > > > In msix_setup_entries(), we get nvecs msi_entry structs, and we > > get a saved .default_irq in each one? > > That's a key point. > > Old-school PCI/MSI is represented by a single interrupt, and you > *could* somehow make it relatively easy for drivers that only > understand INTx to migrate to MSI if you replaced whatever is held in > dev->irq (which should only represent the INTx mapping) with the MSI > interrupt number. Which I guess is what the MSI code is doing. > > This is the 21st century, and nobody should ever rely on such horror, > but I'm sure we do have such drivers in the tree. Boo. > > However, this *cannot* hold true for Multi-MSI, nor MSI-X, because > there is a plurality of interrupts. Even worse, for MSI-X, there is > zero guarantee that the allocated interrupts will be in a contiguous > space. > > Given that, what is dev->irq good for? "Absolutely Nothing! (say it > again!)". > The only thing is that dev->irq is an sysfs ABI to userspace. Due to the inconsistency between legacy PCI INTx, MSI, MSI-X, this ABI should have been absolutely broken nowadays. This is actually what the patchset was originally aiming at to fix. One more question from me is that does dev->irq actually hold any valid hardware INTx information while hardware is using MSI-X? At least in my hardware, sysfs ABI for PCI is all "0". root@ubuntu:/sys/devices/pci0000:7c/0000:7c:00.0/0000:7d:00.3# cat irq 0 root@ubuntu:/sys/devices/pci0000:7c/0000:7c:00.0/0000:7d:00.3# ls -l msi_irqs/* -r--r--r-- 1 root root 4096 Aug 21 22:04 msi_irqs/499 -r--r--r-- 1 root root 4096 Aug 21 22:04 msi_irqs/500 -r--r--r-- 1 root root 4096 Aug 21 22:04 msi_irqs/501 ... root@ubuntu:/sys/devices/pci0000:7c/0000:7c:00.0/0000:7d:00.3# cat msi_irqs/499 msix Not quite sure how it is going on different hardware platforms. > MSI-X is not something you can "accidentally" use. You have to > actively embrace it. In all honesty, this patch tries to move in the > wrong direction. If anything, we should kill this hack altogether and > fix the (handful of?) drivers that rely on it. That'd actually be a > good way to find whether they are still worth keeping in the tree. And > if it breaks too many of them, then at least we'll know where we > stand. > > I'd be tempted to leave the below patch simmer in -next for a few > weeks and see if how many people shout: This looks like a more proper direction to go. but here i am wondering how sysfs ABI document should follow the below change doc is patch 2/2: https://lore.kernel.org/lkml/20210820223744.8439-3-21cnbao@gmail.com/ On the other hand, my feeling is that nobody should depend on sysfs irq entry nowadays. For example, userspace irqbalance is actually using /sys/devices/.../msi_irqs/ So probably we should set this ABI invisible when devices are using MSI or MSI-X? > > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c > index e5e75331b415..2be9a01cbe72 100644 > --- a/drivers/pci/msi.c > +++ b/drivers/pci/msi.c > @@ -591,7 +591,6 @@ msi_setup_entry(struct pci_dev *dev, int nvec, struct irq_affinity *affd) > entry->msi_attrib.is_virtual = 0; > entry->msi_attrib.entry_nr = 0; > entry->msi_attrib.maskbit = !!(control & PCI_MSI_FLAGS_MASKBIT); > - entry->msi_attrib.default_irq = dev->irq; /* Save IOAPIC IRQ */ > entry->msi_attrib.multi_cap = (control & PCI_MSI_FLAGS_QMASK) >> 1; > entry->msi_attrib.multiple = ilog2(__roundup_pow_of_two(nvec)); > > @@ -682,7 +681,6 @@ static int msi_capability_init(struct pci_dev *dev, int nvec, > dev->msi_enabled = 1; > > pcibios_free_irq(dev); > - dev->irq = entry->irq; > return 0; > } > > @@ -742,7 +740,6 @@ static int msix_setup_entries(struct pci_dev *dev, void __iomem *base, > entry->msi_attrib.is_virtual = > entry->msi_attrib.entry_nr >= vec_count; > > - entry->msi_attrib.default_irq = dev->irq; > entry->mask_base = base; > > addr = pci_msix_desc_addr(entry); > @@ -964,8 +961,6 @@ static void pci_msi_shutdown(struct pci_dev *dev) > mask = msi_mask(desc->msi_attrib.multi_cap); > msi_mask_irq(desc, mask, 0); > > - /* Restore dev->irq to its default pin-assertion IRQ */ > - dev->irq = desc->msi_attrib.default_irq; > pcibios_alloc_irq(dev); > } > > diff --git a/include/linux/msi.h b/include/linux/msi.h > index e8bdcb83172b..a631664c1c38 100644 > --- a/include/linux/msi.h > +++ b/include/linux/msi.h > @@ -114,7 +114,6 @@ struct ti_sci_inta_msi_desc { > * @maskbit: [PCI MSI/X] Mask-Pending bit supported? > * @is_64: [PCI MSI/X] Address size: 0=32bit 1=64bit > * @entry_nr: [PCI MSI/X] Entry which is described by this descriptor > - * @default_irq:[PCI MSI/X] The default pre-assigned non-MSI irq > * @mask_pos: [PCI MSI] Mask register position > * @mask_base: [PCI MSI-X] Mask register base address > * @platform: [platform] Platform device specific msi descriptor data > @@ -148,7 +147,6 @@ struct msi_desc { > u8 is_64 : 1; > u8 is_virtual : 1; > u16 entry_nr; > - unsigned default_irq; > } msi_attrib; > union { > u8 mask_pos; > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible. Thanks barry