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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2bd5bd5ef27sm242035275ad.8.2026.05.19.07.40.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 07:40:14 -0700 (PDT) Date: Tue, 19 May 2026 14:40:05 +0000 From: Pranjal Shrivastava To: Samiullah Khawaja Cc: Baolu Lu , David Woodhouse , Joerg Roedel , Will Deacon , Jason Gunthorpe , Robin Murphy , Kevin Tian , Alex Williamson , Shuah Khan , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Saeed Mahameed , Adithya Jayachandran , Parav Pandit , Leon Romanovsky , William Tu , Pratyush Yadav , Pasha Tatashin , David Matlack , Andrew Morton , Chris Li , Vipin Sharma , YiFei Zhu Subject: Re: [PATCH v2 07/16] iommu/vt-d: Implement device and iommu preserve/unpreserve ops Message-ID: References: <20260427175633.1978233-1-skhawaja@google.com> <20260427175633.1978233-8-skhawaja@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, May 18, 2026 at 08:32:42PM +0000, Samiullah Khawaja wrote: > On Fri, May 08, 2026 at 02:36:56AM +0000, Samiullah Khawaja wrote: > > On Thu, May 07, 2026 at 02:25:14PM +0800, Baolu Lu wrote: > > > On 4/28/26 01:56, Samiullah Khawaja wrote: > > > > Add implementation of the device and iommu presevation in a separate > > > > file. Also set the device and iommu preserve/unpreserve ops in the > > > > struct iommu_ops. > > > > > > > > During normal shutdown the iommu translation is disabled. Since the root > > > > table is preserved during live update, it needs to be cleaned up and the > > > > context entries of the unpreserved devices need to be cleared. > > > > > > This is not related to preserve/unpreserve ops and could be made in a > > > separated patch? > > > > Agreed. I will move this stuff to a separate patch. > > > > > > > > > > > Signed-off-by: Samiullah Khawaja > > > > --- > > > > MAINTAINERS | 1 + > > > > drivers/iommu/intel/Makefile | 1 + > > > > drivers/iommu/intel/iommu.c | 52 +++++++++++- > > > > drivers/iommu/intel/iommu.h | 28 +++++++ > > > > drivers/iommu/intel/liveupdate.c | 139 +++++++++++++++++++++++++++++++ > > > > drivers/iommu/iommu.c | 18 ++++ > > > > include/linux/iommu-liveupdate.h | 10 +++ > > > > include/linux/iommu.h | 14 ++++ > > > > include/linux/kho/abi/iommu.h | 18 ++++ > > > > 9 files changed, 277 insertions(+), 4 deletions(-) > > > > create mode 100644 drivers/iommu/intel/liveupdate.c > > > > > > [snip] > > > > > > > +{ > > > > + struct context_entry *context; > > > > + int ret; > > > > + int i; > > > > + > > > > + for (i = 0; i < ROOT_ENTRY_NR; i++) { > > > > + /* > > > > + * Alloc the context tables now to make sure the iommu unit is > > > > + * properly preserved. These might stay unused and wastes around > > > > + * 32MB max in scalable mode. > > > > + */ > > > > > > Instead of allocating and preserving context tables for all root entries > > > (as noted, can waste up to 32MB), could we restrict this only to the > > > entries possibly in use by active PCI devices? > > > > I think the hotplug devices or VFs created through SR-IOV will be missed > > that way. Lets say device A is preserved and the associated iommu is > > also preserved. And then a new device B is hotplugged and preserved, > > then the context table for that will be missed. > > Ok I thought about it a little more and basically we have following > things to consider when we preserve context tables, > > - The devices can be hotplugged and preserved, so the context tables of > those need to be preserved if we don't allocate all of them first time > we preserve iommu, as done here. > - New context tables can be added (after hotplug) for unpreserved > devices. And if we don't get another iommu preserve call after these > are added, those remain unpreserved, so during shutdown those entries > need to be removed from root table or preserved for simplicity. > > To solve this we can, > > 1. Either preserve the new context table when it is added for a preserved > iommu. This can be done in iommu_context_addr(). This is simpler and > no tracking needed. > > 2. Or track the preserved context tables using a bitmap and then preserve > them incremently whenever a device is preserved. On shutdown during > cleanup, we can clear the entries for unpreserved context tables from > root table. > > I am inclined towards second option. WDYT? Thinking out loud here, I agree that shifting away from the 32MB pre-allocation is the right direction. I'm wondering if we can avoid the overhead of introducing a new tracking bitmap (Option 2) altogether? Since the IOMMU serialization is a strict dependency for device tracking, could we move the context table preservation directly into the device level op: intel_iommu_preserve_device()? Whenever a specific device is preserved on-demand: 1. It queries the parent IOMMU to fetch the allocated context table backing its info->bus. 2. It calls iommu_preserve_page(context) for that table. Because KHO's tracking handles duplicates, this should be fine if multiple devices reside on the same bus... Regarding Scalable Mode, we could just need a simple check in that path: /* intel_iommu_preserve_device */ /* Preserve the primary/lower context table backing this bus */ context = iommu_context_addr(info->iommu, info->bus, 0, 0); if (context) iommu_preserve_page(context); /* If scalable mode is active, preserve the upper context table as well */ if (sm_supported(info->iommu)) { context = iommu_context_addr(info->iommu, info->bus, 0x80, 0); if (context) iommu_preserve_page(context); } WDYT? > > I think we will have to do similar stuff for PASID also down the road to > preserve pasid_tables in PASID directory. > > > > Since we don't track the context_tables that are preserved, there is no > > way to incremently preserve the new-ones. Let me look into the behaviour > > of KHO, maybe we can make the preserve call idempotent and do these > > incrementally. > > > > > > > + spin_lock(&iommu->lock); > > > > + context = iommu_context_addr(iommu, i, 0, 1); > > > > + spin_unlock(&iommu->lock); > > > > + if (!context) { > > > > + ret = -ENOMEM; > > > > + goto error; > > > > + } > [snip] Thanks, Praan