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a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1777323389; bh=w4+T1q5j1gjl12AzNykoZ9kgKNsM0AyLqJTGq2x4mJw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=g3klIaNv0aZDwiuY6aSr9d1ovw1UNaC1yS0v955Li3fu510xl6luT8FxEwoEqgsV9 qO5XgODem35nBKQSBw1Y/oPQwo73ezTIvaKLd6m9LDkmCPmXDtkuNmar6v6P8E4uZZ NJTPwgA90pNAQX3lXJdDUBe1VtE8QmuErhznSO4I= Date: Mon, 27 Apr 2026 13:56:25 -0700 From: Jacob Pan To: David Matlack Cc: iommu@lists.linux.dev, kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Rientjes , Jason Gunthorpe , Joerg Roedel , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pranjal Shrivastava , Pratyush Yadav , Robin Murphy , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Will Deacon , William Tu , Yi Liu , jacob.pan@linux.microsoft.com Subject: Re: [PATCH v4 08/11] PCI: liveupdate: Require preserved devices are in immutable singleton IOMMU groups Message-ID: <20260427135625.0000413e@linux.microsoft.com> In-Reply-To: <20260423212316.3431746-9-dmatlack@google.com> References: <20260423212316.3431746-1-dmatlack@google.com> <20260423212316.3431746-9-dmatlack@google.com> Organization: LSG X-Mailer: Claws Mail 3.21.0 (GTK+ 2.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 219D480011 X-Stat-Signature: bdih5jo9a8fipox9my38phuyhf171ky8 X-Rspam-User: X-HE-Tag: 1777323389-226082 X-HE-Meta: U2FsdGVkX1/jgHVR0fk/CykeM0h5Mm6kOiRt8MVkOvk+rKhOO1FFpOvaUk8rJ2sgUu4ypbyVVoFtfVDr1pK6lZNv9QGxdouVF74UBrwg6bIl/KCiVxuNi6MXUKJtWRGb2agwXRcFbd6CU+JYUYPBmNnnn77hj4YLNykPuNXE1+imOQeKr8SSkLiWdrl61hRjSAeyk3mqNfpxI+cfe5086CGYb0kCOYdb6B9+vUOV9COYNCtym1PFKXtcHQExKfMhkYXDnKr4eLsm0xMBsb+EyyCQTvHyUUxV6FtkZgy10JqrJ9MtHJIGXDd1BiVDnazpHSx3sGBLaJ34X0jruft9tRihjo/qDlVMUUAyxl6OpSIDnCgm6NA4tBZ/8cbuIc8ym7cKtrgPkM3wv8nvCe42wsKZ6Dp4qHwVZArVrB6To0DrSZem3t4RJXHB16PYHesiDEHsfdMk9pfOLjaERuzCjjs2rWSNy32cfngYdl4p3GoascEoUPLJmbJKciYhF9N+nP8kaOeSkQQIC7ExnhX66UXWQfhKR1zja3Ey+LtaB67osgWv2/272YJzY3OMGHtlLNdWrDJX3gp/A84ybOYuerVRclirvw71hsJIksTv/keANv7LDD67vdHwnJBcBUvcmUN6fqpNJZmHUvSBEJSAIBAaqQezHJzIzQJ8MogGFsmigcqfd7YCgpJUxrXKy5foSO8rJdxeavf3HS3GJUOAyStUWYZXtUxFITYVHIF9wbqLLMvGbcpzAIlQm9ft3i+S45O6wSfKpwBdX5p3vyLpLZ+wY3G8jnYEXS14jfa/pgTWEaFk+/NjobQTsxFD/liDu756LWSQnwaeTm/f4VjLE/pF06zbALB7SMqLI5e9YH1wVK4eg/iSvaQ5pCPv5nmwVfU0ycTuwmpzWREHRSJUHmgccdIcPABmmZp3LYhl0x8/DlL6uY/vcxd2Wu7p0mvlwo5Xvw0sQ1yaRy4iDT5 M18zFgrY lJGJTAmTagBQ+pE0bFNRP9O2X39R2DwdfkZeQT33H8ZdNWPwhi5UxQfo6nhu2G+ozrv9a2acQwqxzJQkY1xt62TsuxpSnYhao6fs555XKj01N9SECMPLI05DK3lahCvg2qkaHeMGJ+B5cw4Zb5zECU6ry+SLEG9H4a9rFRV154d1sjpuU7t8SIwlOQUf/bFTY+VwBolfeDq4c7Ce7C7u8IYyNr2Nnk8VQEwvlIe4RQW3odj9c6oKwYDCL2SZf39kLOHPsApoLwzClz42mS7RwprVZIoKAPsOMPjeNUV2j8zh/pkKG4WZEDpmb+tgDmjwWObaEdInzflQbYutgLeVpKzwtWy6eGE5EuYbEgr16Jurk9duu7bAi3RRD57+PjjVGdiJ0+V7D8ORkJYj2b7jNqdMkyQAfk9+LP7pYtAS3p1ZzUjY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi David, On Thu, 23 Apr 2026 21:23:12 +0000 David Matlack wrote: > Restrict support for preserving PCI devices across Live Update to > devices in immutable singleton IOMMU groups. A device's group is > considered immutable if all bridges upstream from the device up to the > root port have the required ACS features enabled. > > Since ACS flags are inherited across a Live Update for preserved > devices and all the way up to the root port, the preserved device > should be in a singleton IOMMU group after kexec in the new kernel. > > This change should still permit all the current use-cases for PCI > device preservation across Live Update, since it is intended to be > used in Cloud enviroments which should have the required ACS features > enabled for virtualization purposes. > > If a device is part of a multi-device IOMMU group, preserving it will > now fail with an error. This restriction may be lifted in the future > if support for preserving multi-device groups is desired. > > Signed-off-by: David Matlack > --- > drivers/iommu/iommu.c | 35 +++++++++++++++++++++++++++++++++++ > drivers/pci/liveupdate.c | 6 ++++++ > include/linux/iommu.h | 7 +++++++ > 3 files changed, 48 insertions(+) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 61c12ba78206..782e73a9d45f 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -1664,6 +1664,41 @@ struct iommu_group *pci_device_group(struct > device *dev) } > EXPORT_SYMBOL_GPL(pci_device_group); > > +bool pci_device_group_immutable_singleton(struct pci_dev *dev) > +{ > + struct iommu_group *group; > + struct group_device *d; > + struct pci_bus *bus; > + int nr_devices = 0; > + > + group = iommu_group_get(&dev->dev); > + if (!group) > + return false; This may not work for noiommu mode where we could have a null group. Maybe I can add special case later? > + mutex_lock(&group->mutex); > + > + for_each_group_device(group, d) > + nr_devices++; > + > + mutex_unlock(&group->mutex); > + iommu_group_put(group); nit: scoped_guard(mutex, &group->mutex) { for_each_group_device(group, d) nr_devices++; } > + > + if (nr_devices != 1) > + return false; > + > + for (bus = dev->bus; !pci_is_root_bus(bus); bus = > bus->parent) { > + if (!bus->self) > + continue; > + > + if (!pci_acs_path_enabled(bus->self, NULL, > REQ_ACS_FLAGS)) > + return false; > + > + break; > + } > + > + return true; > +} > + > /* Get the IOMMU group for device on fsl-mc bus */ > struct iommu_group *fsl_mc_device_group(struct device *dev) > { > diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c > index a9a89f7bd3e5..54a90ff02bdd 100644 > --- a/drivers/pci/liveupdate.c > +++ b/drivers/pci/liveupdate.c > @@ -133,6 +133,7 @@ > #define pr_fmt(fmt) "PCI: liveupdate: " fmt > > #include > +#include > #include > #include > #include > @@ -359,6 +360,11 @@ int pci_liveupdate_preserve(struct pci_dev *dev) > if (dev->is_virtfn) > return -EINVAL; > > + if (!pci_device_group_immutable_singleton(dev)) { > + pci_warn(dev, "Device preservation limited to > immutable singleton iommu groups\n"); > + return -EINVAL; > + } > + > if (dev->liveupdate_outgoing) > return -EBUSY; > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index e587d4ac4d33..6f5d1dec3f89 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -1096,6 +1096,8 @@ extern struct iommu_group > *generic_device_group(struct device *dev); struct iommu_group > *fsl_mc_device_group(struct device *dev); extern struct iommu_group > *generic_single_device_group(struct device *dev); > +bool pci_device_group_immutable_singleton(struct pci_dev *dev); > + > /** > * struct iommu_fwspec - per-device IOMMU instance data > * @iommu_fwnode: firmware handle for this device's IOMMU > @@ -1528,6 +1530,11 @@ static inline int > pci_dev_reset_iommu_prepare(struct pci_dev *pdev) static inline void > pci_dev_reset_iommu_done(struct pci_dev *pdev) { > } > + > +static inline bool pci_device_group_immutable_singleton(struct > pci_dev *dev) +{ > + return false; > +} > #endif /* CONFIG_IOMMU_API */ > > #ifdef CONFIG_IRQ_MSI_IOMMU