On Wed, 14 Apr 2021 12:50:52 +0100 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > That said, I think we need to have a quicker fix for the immediate > > issue with 64-bit bit dma_addr on 32-bit arch and the misalignment hole > > it leaves[3] in struct page. In[3] you mention ppc32, does it only > > happens on certain 32-bit archs? > > AFAICT it happens on mips32, ppc32, arm32 and arc. It doesn't happen > on x86-32 because dma_addr_t is 32-bit aligned. (If others want to reproduce). First I could not reproduce on ARM32. Then I found out that enabling CONFIG_XEN on ARCH=arm was needed to cause the issue by enabling CONFIG_ARCH_DMA_ADDR_T_64BIT. Details below signature. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer >From file: arch/arm/Kconfig config XEN bool "Xen guest support on ARM" depends on ARM && AEABI && OF depends on CPU_V7 && !CPU_V6 depends on !GENERIC_ATOMIC64 depends on MMU select ARCH_DMA_ADDR_T_64BIT select ARM_PSCI select SWIOTLB select SWIOTLB_XEN select PARAVIRT help Say Y if you want to run Linux in a Virtual Machine on Xen on ARM. My make compile command: export VERSION=gcc-arm-10.2-2020.11-x86_64-arm-none-linux-gnueabihf/ export CROSS_COMPILE="/home/${USER}/cross-compilers/${VERSION}/bin/arm-none-linux-gnueabihf-" make -j8 ARCH=arm CROSS_COMPILE=$CROSS_COMPILE Pahole output: $ pahole -C page mm/page_alloc.o struct page { long unsigned int flags; /* 0 4 */ /* XXX 4 bytes hole, try to pack */ union { struct { struct list_head lru; /* 8 8 */ struct address_space * mapping; /* 16 4 */ long unsigned int index; /* 20 4 */ long unsigned int private; /* 24 4 */ }; /* 8 20 */ struct { dma_addr_t dma_addr; /* 8 8 */ }; /* 8 8 */ struct { union { struct list_head slab_list; /* 8 8 */ struct { struct page * next; /* 8 4 */ short int pages; /* 12 2 */ short int pobjects; /* 14 2 */ }; /* 8 8 */ }; /* 8 8 */ struct kmem_cache * slab_cache; /* 16 4 */ void * freelist; /* 20 4 */ union { void * s_mem; /* 24 4 */ long unsigned int counters; /* 24 4 */ struct { unsigned int inuse:16; /* 24: 0 4 */ unsigned int objects:15; /* 24:16 4 */ unsigned int frozen:1; /* 24:31 4 */ }; /* 24 4 */ }; /* 24 4 */ }; /* 8 20 */ struct { long unsigned int compound_head; /* 8 4 */ unsigned char compound_dtor; /* 12 1 */ unsigned char compound_order; /* 13 1 */ /* XXX 2 bytes hole, try to pack */ atomic_t compound_mapcount; /* 16 4 */ unsigned int compound_nr; /* 20 4 */ }; /* 8 16 */ struct { long unsigned int _compound_pad_1; /* 8 4 */ atomic_t hpage_pinned_refcount; /* 12 4 */ struct list_head deferred_list; /* 16 8 */ }; /* 8 16 */ struct { long unsigned int _pt_pad_1; /* 8 4 */ pgtable_t pmd_huge_pte; /* 12 4 */ long unsigned int _pt_pad_2; /* 16 4 */ union { struct mm_struct * pt_mm; /* 20 4 */ atomic_t pt_frag_refcount; /* 20 4 */ }; /* 20 4 */ spinlock_t ptl; /* 24 4 */ }; /* 8 20 */ struct { struct dev_pagemap * pgmap; /* 8 4 */ void * zone_device_data; /* 12 4 */ }; /* 8 8 */ struct callback_head callback_head __attribute__((__aligned__(4))); /* 8 8 */ } __attribute__((__aligned__(8))); /* 8 24 */ union { atomic_t _mapcount; /* 32 4 */ unsigned int page_type; /* 32 4 */ unsigned int active; /* 32 4 */ int units; /* 32 4 */ }; /* 32 4 */ atomic_t _refcount; /* 36 4 */ /* size: 40, cachelines: 1, members: 4 */ /* sum members: 36, holes: 1, sum holes: 4 */ /* forced alignments: 1, forced holes: 1, sum forced holes: 4 */ /* last cacheline: 40 bytes */ } __attribute__((__aligned__(8)));
