From: Peter Xu <peterx@redhat.com> mainline inclusion from mainline-v6.12-rc1 commit 6857be5fecaebd9773ff27b6d29b6fff3b1abbce category: feature bugzilla: https://gitee.com/src-openeuler/kernel/issues/ID4NL4 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- Patch series "mm: Support huge pfnmaps", v2. Overview ======== This series implements huge pfnmaps support for mm in general. Huge pfnmap allows e.g. VM_PFNMAP vmas to map in either PMD or PUD levels, similar to what we do with dax / thp / hugetlb so far to benefit from TLB hits. Now we extend that idea to PFN mappings, e.g. PCI MMIO bars where it can grow as large as 8GB or even bigger. Currently, only x86_64 (1G+2M) and arm64 (2M) are supported. The last patch (from Alex Williamson) will be the first user of huge pfnmap, so as to enable vfio-pci driver to fault in huge pfn mappings. Implementation ============== In reality, it's relatively simple to add such support comparing to many other types of mappings, because of PFNMAP's specialties when there's no vmemmap backing it, so that most of the kernel routines on huge mappings should simply already fail for them, like GUPs or old-school follow_page() (which is recently rewritten to be folio_walk* APIs by David). One trick here is that we're still unmature on PUDs in generic paths here and there, as DAX is so far the only user. This patchset will add the 2nd user of it. Hugetlb can be a 3rd user if the hugetlb unification work can go on smoothly, but to be discussed later. The other trick is how to allow gup-fast working for such huge mappings even if there's no direct sign of knowing whether it's a normal page or MMIO mapping. This series chose to keep the pte_special solution, so that it reuses similar idea on setting a special bit to pfnmap PMDs/PUDs so that gup-fast will be able to identify them and fail properly. Along the way, we'll also notice that the major pgtable pfn walker, aka, follow_pte(), will need to retire soon due to the fact that it only works with ptes. A new set of simple API is introduced (follow_pfnmap* API) to be able to do whatever follow_pte() can already do, plus that it can also process huge pfnmaps now. Half of this series is about that and converting all existing pfnmap walkers to use the new API properly. Hopefully the new API also looks better to avoid exposing e.g. pgtable lock details into the callers, so that it can be used in an even more straightforward way. Here, three more options will be introduced and involved in huge pfnmap: - ARCH_SUPPORTS_HUGE_PFNMAP Arch developers will need to select this option when huge pfnmap is supported in arch's Kconfig. After this patchset applied, both x86_64 and arm64 will start to enable it by default. - ARCH_SUPPORTS_PMD_PFNMAP / ARCH_SUPPORTS_PUD_PFNMAP These options are for driver developers to identify whether current arch / config supports huge pfnmaps, making decision on whether it can use the huge pfnmap APIs to inject them. One can refer to the last vfio-pci patch from Alex on the use of them properly in a device driver. So after the whole set applied, and if one would enable some dynamic debug lines in vfio-pci core files, we should observe things like: vfio-pci 0000:00:06.0: vfio_pci_mmap_huge_fault(,order = 9) BAR 0 page offset 0x0: 0x100 vfio-pci 0000:00:06.0: vfio_pci_mmap_huge_fault(,order = 9) BAR 0 page offset 0x200: 0x100 vfio-pci 0000:00:06.0: vfio_pci_mmap_huge_fault(,order = 9) BAR 0 page offset 0x400: 0x100 In this specific case, it says that vfio-pci faults in PMDs properly for a few BAR0 offsets. Patch Layout ============ Patch 1: Introduce the new options mentioned above for huge PFNMAPs Patch 2: A tiny cleanup Patch 3-8: Preparation patches for huge pfnmap (include introduce special bit for pmd/pud) Patch 9-16: Introduce follow_pfnmap*() API, use it everywhere, and then drop follow_pte() API Patch 17: Add huge pfnmap support for x86_64 Patch 18: Add huge pfnmap support for arm64 Patch 19: Add vfio-pci support for all kinds of huge pfnmaps (Alex) TODO ==== More architectures / More page sizes ------------------------------------ Currently only x86_64 (2M+1G) and arm64 (2M) are supported. There seems to have plan to support arm64 1G later on top of this series [2]. Any arch will need to first support THP / THP_1G, then provide a special bit in pmds/puds to support huge pfnmaps. remap_pfn_range() support ------------------------- Currently, remap_pfn_range() still only maps PTEs. With the new option, remap_pfn_range() can logically start to inject either PMDs or PUDs when the alignment requirements match on the VAs. When the support is there, it should be able to silently benefit all drivers that is using remap_pfn_range() in its mmap() handler on better TLB hit rate and overall faster MMIO accesses similar to processor on hugepages. More driver support ------------------- VFIO is so far the only consumer for the huge pfnmaps after this series applied. Besides above remap_pfn_range() generic optimization, device driver can also try to optimize its mmap() on a better VA alignment for either PMD/PUD sizes. This may, iiuc, normally require userspace changes, as the driver doesn't normally decide the VA to map a bar. But I don't think I know all the drivers to know the full picture. Credits all go to Alex on help testing the GPU/NIC use cases above. [0] https://lore.kernel.org/r/73ad9540-3fb8-4154-9a4f-30a0a2b03d41@lucifer.local [1] https://lore.kernel.org/r/20240807194812.819412-1-peterx@redhat.com [2] https://lore.kernel.org/r/498e0731-81a4-4f75-95b4-a8ad0bcc7665@huawei.com This patch (of 19): This patch introduces the option to introduce special pte bit into pmd/puds. Archs can start to define pmd_special / pud_special when supported by selecting the new option. Per-arch support will be added later. Before that, create fallbacks for these helpers so that they are always available. Link: https://lkml.kernel.org/r/20240826204353.2228736-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20240826204353.2228736-2-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Gavin Shan <gshan@redhat.com> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Niklas Schnelle <schnelle@linux.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Sean Christopherson <seanjc@google.com> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will@kernel.org> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: include/linux/mm.h [Context conflicts.] Signed-off-by: Yin Tirui <yintirui@huawei.com> --- include/linux/mm.h | 24 ++++++++++++++++++++++++ mm/Kconfig | 13 +++++++++++++ 2 files changed, 37 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index e364a2846a78..f0efb11b915d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2779,6 +2779,30 @@ static inline pte_t pte_mkspecial(pte_t pte) } #endif +#ifndef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP +static inline bool pmd_special(pmd_t pmd) +{ + return false; +} + +static inline pmd_t pmd_mkspecial(pmd_t pmd) +{ + return pmd; +} +#endif /* CONFIG_ARCH_SUPPORTS_PMD_PFNMAP */ + +#ifndef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP +static inline bool pud_special(pud_t pud) +{ + return false; +} + +static inline pud_t pud_mkspecial(pud_t pud) +{ + return pud; +} +#endif /* CONFIG_ARCH_SUPPORTS_PUD_PFNMAP */ + #ifndef CONFIG_ARCH_HAS_PTE_DEVMAP static inline int pte_devmap(pte_t pte) { diff --git a/mm/Kconfig b/mm/Kconfig index 5972d143fb2b..4eb0642b71e5 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -903,6 +903,19 @@ endif # TRANSPARENT_HUGEPAGE config PGTABLE_HAS_HUGE_LEAVES def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE +# TODO: Allow to be enabled without THP +config ARCH_SUPPORTS_HUGE_PFNMAP + def_bool n + depends on TRANSPARENT_HUGEPAGE + +config ARCH_SUPPORTS_PMD_PFNMAP + def_bool y + depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE + +config ARCH_SUPPORTS_PUD_PFNMAP + def_bool y + depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD + # # UP and nommu archs use km based percpu allocator # -- 2.43.0