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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF2FFC433F5 for ; Wed, 13 Oct 2021 18:27:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CDF7860EE9 for ; Wed, 13 Oct 2021 18:27:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235412AbhJMS3N (ORCPT ); Wed, 13 Oct 2021 14:29:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:60454 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229814AbhJMS3N (ORCPT ); Wed, 13 Oct 2021 14:29:13 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 52D6D60C49; Wed, 13 Oct 2021 18:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634149629; bh=0KaxqBpPYtBpR05jXKW1Op9xgdPeY4wuR3VX8HO8Yug=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=FIxQNrdc60xMqLc8svzrhC1Ia2JmTjEC2KvqlXNDX1MD77r2c9NY0a2ASgaCstVxW maCg0Pa6KUPMJktX9Kekr5KQuKzXG4dNAKjPgcbUhJf1FEj+RbPqlnqLhmEyOTVChk Fl4wUi2sF2/ncJgl4CQiSCy5aDZXsLudht4eFwTYeHXbqU5lW2LReRjsmNG+o663n6 0ZwJDI+J4aGH7XraGw+8ZD/TYGfJbQAJSWAiWSW9pZ4ev1e7wknnhoMbPa4YVtIbHL +hQdIK4jnr+9yIMUdoiJ3T9BgVrnoLfPadWDnK1114lmJND8FpvLLkZkbP4YlaUY7Q JcEnlPhWOMRzw== Date: Wed, 13 Oct 2021 13:27:07 -0500 From: Bjorn Helgaas To: Yishai Hadas Cc: alex.williamson@redhat.com, bhelgaas@google.com, jgg@nvidia.com, saeedm@nvidia.com, linux-pci@vger.kernel.org, kvm@vger.kernel.org, netdev@vger.kernel.org, kuba@kernel.org, leonro@nvidia.com, kwankhede@nvidia.com, mgurtovoy@nvidia.com, maorg@nvidia.com Subject: Re: [PATCH V1 mlx5-next 04/13] PCI/IOV: Allow SRIOV VF drivers to reach the drvdata of a PF Message-ID: <20211013182707.GA1906754@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211013094707.163054-5-yishaih@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Oct 13, 2021 at 12:46:58PM +0300, Yishai Hadas wrote: > From: Jason Gunthorpe > > There are some cases where a SRIOV VF driver will need to reach into and > interact with the PF driver. This requires accessing the drvdata of the PF. > > Provide a function pci_iov_get_pf_drvdata() to return this PF drvdata in a > safe way. Normally accessing a drvdata of a foreign struct device would be > done using the device_lock() to protect against device driver > probe()/remove() races. > > However, due to the design of pci_enable_sriov() this will result in a > ABBA deadlock on the device_lock as the PF's device_lock is held during PF > sriov_configure() while calling pci_enable_sriov() which in turn holds the > VF's device_lock while calling VF probe(), and similarly for remove. > > This means the VF driver can never obtain the PF's device_lock. > > Instead use the implicit locking created by pci_enable/disable_sriov(). A > VF driver can access its PF drvdata only while its own driver is attached, > and the PF driver can control access to its own drvdata based on when it > calls pci_enable/disable_sriov(). > > To use this API the PF driver will setup the PF drvdata in the probe() > function. pci_enable_sriov() is only called from sriov_configure() which > cannot happen until probe() completes, ensuring no VF races with drvdata > setup. > > For removal, the PF driver must call pci_disable_sriov() in its remove > function before destroying any of the drvdata. This ensures that all VF > drivers are unbound before returning, fencing concurrent access to the > drvdata. > > The introduction of a new function to do this access makes clear the > special locking scheme and the documents the requirements on the PF/VF > drivers using this. > > Signed-off-by: Jason Gunthorpe > Signed-off-by: Leon Romanovsky > Signed-off-by: Yishai Hadas Acked-by: Bjorn Helgaas Nit: s/SRIOV/SR-IOV/ above so it matches usage in the spec. I think it's nice to include the actual interface in the subject when practical. > --- > drivers/pci/iov.c | 29 +++++++++++++++++++++++++++++ > include/linux/pci.h | 7 +++++++ > 2 files changed, 36 insertions(+) > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c > index e7751fa3fe0b..ca696730f761 100644 > --- a/drivers/pci/iov.c > +++ b/drivers/pci/iov.c > @@ -47,6 +47,35 @@ int pci_iov_vf_id(struct pci_dev *dev) > } > EXPORT_SYMBOL_GPL(pci_iov_vf_id); > > +/** > + * pci_iov_get_pf_drvdata - Return the drvdata of a PF > + * @dev - VF pci_dev > + * @pf_driver - Device driver required to own the PF > + * > + * This must be called from a context that ensures that a VF driver is attached. > + * The value returned is invalid once the VF driver completes its remove() > + * callback. > + * > + * Locking is achieved by the driver core. A VF driver cannot be probed until > + * pci_enable_sriov() is called and pci_disable_sriov() does not return until > + * all VF drivers have completed their remove(). > + * > + * The PF driver must call pci_disable_sriov() before it begins to destroy the > + * drvdata. > + */ > +void *pci_iov_get_pf_drvdata(struct pci_dev *dev, struct pci_driver *pf_driver) > +{ > + struct pci_dev *pf_dev; > + > + if (dev->is_physfn) > + return ERR_PTR(-EINVAL); > + pf_dev = dev->physfn; > + if (pf_dev->driver != pf_driver) > + return ERR_PTR(-EINVAL); > + return pci_get_drvdata(pf_dev); > +} > +EXPORT_SYMBOL_GPL(pci_iov_get_pf_drvdata); > + > /* > * Per SR-IOV spec sec 3.3.10 and 3.3.11, First VF Offset and VF Stride may > * change when NumVFs changes. > diff --git a/include/linux/pci.h b/include/linux/pci.h > index 2337512e67f0..639a0a239774 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -2154,6 +2154,7 @@ void __iomem *pci_ioremap_wc_bar(struct pci_dev *pdev, int bar); > int pci_iov_virtfn_bus(struct pci_dev *dev, int id); > int pci_iov_virtfn_devfn(struct pci_dev *dev, int id); > int pci_iov_vf_id(struct pci_dev *dev); > +void *pci_iov_get_pf_drvdata(struct pci_dev *dev, struct pci_driver *pf_driver); > int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn); > void pci_disable_sriov(struct pci_dev *dev); > > @@ -2187,6 +2188,12 @@ static inline int pci_iov_vf_id(struct pci_dev *dev) > return -ENOSYS; > } > > +static inline void *pci_iov_get_pf_drvdata(struct pci_dev *dev, > + struct pci_driver *pf_driver) > +{ > + return ERR_PTR(-EINVAL); > +} > + > static inline int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn) > { return -ENODEV; } > > -- > 2.18.1 >