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Sashiko AI review found 2 potential issues to consider: - [Medium] iommu/dma: CONFIG_PISA breaks builds on 64-bit UML and !SPARSEMEM - [Medium] iommu/dma: pisa_meta_memory_cb() ignores pisa_meta_prealloc() error -- commit 4571e9a5a4e068f2cb559f5c16306bf2b33d6515 Author: Luigi Rizzo iommu/dma: Introduce CONFIG_PISA and metadata table This commit introduces the CONFIG_PISA build option, a sparse per-2MB-frame metadata table in drivers/iommu/pisa-meta.c, and KUnit tests for metadata table operations. > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig > index 85a8d7fdfa30b..15e06eaed0924 100644 > --- a/drivers/iommu/Kconfig > +++ b/drivers/iommu/Kconfig > @@ -423,4 +423,37 @@ config IOMMU_DEBUG_PAGEALLOC > If unsure, say N. > endif # IOMMU_SUPPORT > =20 > +# Pre-mapped IOVA Superpage Allocator > +config PISA > + bool "Pre-mapped IOVA Superpage Allocator" > + depends on X86_64 || ARM64 > + depends on !PREEMPT_RT > + default y [Severity: Medium] Can enabling CONFIG_PISA by default break builds on 64-bit UML (ARCH=3Dum on x86_64) or configurations without CONFIG_SPARSEMEM? PISA is placed outside the IOMMU_SUPPORT block, and drivers/Makefile enters drivers/iommu/ unconditionally. In drivers/iommu/pisa-meta.c, static_assert(PISA_SHIFT <=3D SUBSECTION_SHIFT) and pisa_meta_init()'s use = of MAX_PHYSMEM_BITS both rely on symbols that are only defined when CONFIG_SPARSEMEM is enabled, whereas 64-bit UML sets CONFIG_X86_64=3Dy with CONFIG_FLATMEM=3Dy. > diff --git a/drivers/iommu/pisa-meta.c b/drivers/iommu/pisa-meta.c > new file mode 100644 > index 0000000000000..5ceea91e4d5e8 > --- /dev/null > +++ b/drivers/iommu/pisa-meta.c [ ... ] > +/* Page tables for memory about to go online; failure keeps it out of th= e allocators. */ > +static int pisa_meta_memory_cb(struct notifier_block *nb, unsigned long = action, void *arg) > +{ > + struct memory_notify *mn =3D arg; > + > + if (action !=3D MEM_GOING_ONLINE) > + return NOTIFY_OK; > + > + mutex_lock(&pisa_meta_mutex); > + if (pisa_meta_array) > + pisa_meta_prealloc(pisa_meta_array, pisa_meta_nframes, mn->start_pfn, > + mn->start_pfn + mn->nr_pages); > + mutex_unlock(&pisa_meta_mutex); > + return NOTIFY_OK; > +} [Severity: Medium] Should pisa_meta_memory_cb() propagate errors from pisa_meta_prealloc() via notifier_from_errno()? Returning NOTIFY_OK unconditionally allows online_pages() to bring hotplugg= ed memory online even when page-table preallocation fails. Any subsequent non-blocking pisa_meta_ensure_pfn(pfn, false) call on a page from that range cannot allocate the missing page table and fails with -EINVAL in pisa_meta_back(). --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261109182533.3594= 984-1-lrizzo@google.com?part=3D1