6.12-stable review patch. If anyone has any objections, please let me know.
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From: Lu Baolu baolu.lu@linux.intel.com
commit 12724ce3fe1a3d8f30d56e48b4f272d8860d1970 upstream.
The iotlb_sync_map iommu ops allows drivers to perform necessary cache flushes when new mappings are established. For the Intel iommu driver, this callback specifically serves two purposes:
- To flush caches when a second-stage page table is attached to a device whose iommu is operating in caching mode (CAP_REG.CM==1). - To explicitly flush internal write buffers to ensure updates to memory- resident remapping structures are visible to hardware (CAP_REG.RWBF==1).
However, in scenarios where neither caching mode nor the RWBF flag is active, the cache_tag_flush_range_np() helper, which is called in the iotlb_sync_map path, effectively becomes a no-op.
Despite being a no-op, cache_tag_flush_range_np() involves iterating through all cache tags of the iommu's attached to the domain, protected by a spinlock. This unnecessary execution path introduces overhead, leading to a measurable I/O performance regression. On systems with NVMes under the same bridge, performance was observed to drop from approximately ~6150 MiB/s down to ~4985 MiB/s.
Introduce a flag in the dmar_domain structure. This flag will only be set when iotlb_sync_map is required (i.e., when CM or RWBF is set). The cache_tag_flush_range_np() is called only for domains where this flag is set. This flag, once set, is immutable, given that there won't be mixed configurations in real-world scenarios where some IOMMUs in a system operate in caching mode while others do not. Theoretically, the immutability of this flag does not impact functionality.
Reported-by: Ioanna Alifieraki ioanna-maria.alifieraki@canonical.com Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2115738 Link: https://lore.kernel.org/r/20250701171154.52435-1-ioanna-maria.alifieraki@can... Fixes: 129dab6e1286 ("iommu/vt-d: Use cache_tag_flush_range_np() in iotlb_sync_map") Cc: stable@vger.kernel.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com Reviewed-by: Kevin Tian kevin.tian@intel.com Link: https://lore.kernel.org/r/20250703031545.3378602-1-baolu.lu@linux.intel.com Link: https://lore.kernel.org/r/20250714045028.958850-3-baolu.lu@linux.intel.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iommu/intel/iommu.c | 19 ++++++++++++++++++- drivers/iommu/intel/iommu.h | 3 +++ 2 files changed, 21 insertions(+), 1 deletion(-)
--- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1957,6 +1957,18 @@ static bool dev_is_real_dma_subdevice(st pci_real_dma_dev(to_pci_dev(dev)) != to_pci_dev(dev); }
+static bool domain_need_iotlb_sync_map(struct dmar_domain *domain, + struct intel_iommu *iommu) +{ + if (cap_caching_mode(iommu->cap) && !domain->use_first_level) + return true; + + if (rwbf_quirk || cap_rwbf(iommu->cap)) + return true; + + return false; +} + static int dmar_domain_attach_device(struct dmar_domain *domain, struct device *dev) { @@ -1994,6 +2006,8 @@ static int dmar_domain_attach_device(str if (ret) goto out_block_translation;
+ domain->iotlb_sync_map |= domain_need_iotlb_sync_map(domain, iommu); + return 0;
out_block_translation: @@ -4278,7 +4292,10 @@ static bool risky_device(struct pci_dev static int intel_iommu_iotlb_sync_map(struct iommu_domain *domain, unsigned long iova, size_t size) { - cache_tag_flush_range_np(to_dmar_domain(domain), iova, iova + size - 1); + struct dmar_domain *dmar_domain = to_dmar_domain(domain); + + if (dmar_domain->iotlb_sync_map) + cache_tag_flush_range_np(dmar_domain, iova, iova + size - 1);
return 0; } --- a/drivers/iommu/intel/iommu.h +++ b/drivers/iommu/intel/iommu.h @@ -614,6 +614,9 @@ struct dmar_domain { u8 has_mappings:1; /* Has mappings configured through * iommu_map() interface. */ + u8 iotlb_sync_map:1; /* Need to flush IOTLB cache or write + * buffer when creating mappings. + */
spinlock_t lock; /* Protect device tracking lists */ struct list_head devices; /* all devices' list */