[PATCH fixes] riscv: mm: Do not call pmd dtor on vmemmap page table teardown

[Alexandre Ghiti]

Hi Björn,

On 20/11/2024 14:12, Björn Töpel wrote:
> From: Björn Töpel <bjorn at rivosinc.com>
>
> The vmemmap's, which is used for RV64 with SPARSEMEM_VMEMMAP, page
> tables are populated using pmd (page middle directory) hugetables.
> However, the pmd allocation is not using the generic mechanism used by
> the VMA code (e.g. pmd_alloc()), or the RISC-V specific
> create_pgd_mapping()/alloc_pmd_late(). Instead, the vmemmap page table
> code allocates a page, and calls vmemmap_set_pmd(). This results in
> that the pmd ctor is *not* called, nor would it make sense to do so.
>
> Now, when tearing down a vmemmap page table pmd, the cleanup code
> would unconditionally, and incorrectly call the pmd dtor, which
> results in a crash (best case).
>
> This issue was found when running the HMM selftests:
>
>    | tools/testing/selftests/mm# ./test_hmm.sh smoke
>    | ... # when unloading the test_hmm.ko module
>    | page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10915b
>    | flags: 0x1000000000000000(node=0|zone=1)
>    | raw: 1000000000000000 0000000000000000 dead000000000122 0000000000000000
>    | raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
>    | page dumped because: VM_BUG_ON_PAGE(ptdesc->pmd_huge_pte)
>    | ------------[ cut here ]------------
>    | kernel BUG at include/linux/mm.h:3080!
>    | Kernel BUG [#1]
>    | Modules linked in: test_hmm(-) sch_fq_codel fuse drm drm_panel_orientation_quirks backlight dm_mod
>    | CPU: 1 UID: 0 PID: 514 Comm: modprobe Tainted: G        W          6.12.0-00982-gf2a4f1682d07 #2
>    | Tainted: [W]=WARN
>    | Hardware name: riscv-virtio qemu/qemu, BIOS 2024.10 10/01/2024
>    | epc : remove_pgd_mapping+0xbec/0x1070
>    |  ra : remove_pgd_mapping+0xbec/0x1070
>    | epc : ffffffff80010a68 ra : ffffffff80010a68 sp : ff20000000a73940
>    |  gp : ffffffff827b2d88 tp : ff6000008785da40 t0 : ffffffff80fbce04
>    |  t1 : 0720072007200720 t2 : 706d756420656761 s0 : ff20000000a73a50
>    |  s1 : ff6000008915cff8 a0 : 0000000000000039 a1 : 0000000000000008
>    |  a2 : ff600003fff0de20 a3 : 0000000000000000 a4 : 0000000000000000
>    |  a5 : 0000000000000000 a6 : c0000000ffffefff a7 : ffffffff824469b8
>    |  s2 : ff1c0000022456c0 s3 : ff1ffffffdbfffff s4 : ff6000008915c000
>    |  s5 : ff6000008915c000 s6 : ff6000008915c000 s7 : ff1ffffffdc00000
>    |  s8 : 0000000000000001 s9 : ff1ffffffdc00000 s10: ffffffff819a31f0
>    |  s11: ffffffffffffffff t3 : ffffffff8000c950 t4 : ff60000080244f00
>    |  t5 : ff60000080244000 t6 : ff20000000a73708
>    | status: 0000000200000120 badaddr: ffffffff80010a68 cause: 0000000000000003
>    | [<ffffffff80010a68>] remove_pgd_mapping+0xbec/0x1070
>    | [<ffffffff80fd238e>] vmemmap_free+0x14/0x1e
>    | [<ffffffff8032e698>] section_deactivate+0x220/0x452
>    | [<ffffffff8032ef7e>] sparse_remove_section+0x4a/0x58
>    | [<ffffffff802f8700>] __remove_pages+0x7e/0xba
>    | [<ffffffff803760d8>] memunmap_pages+0x2bc/0x3fe
>    | [<ffffffff02a3ca28>] dmirror_device_remove_chunks+0x2ea/0x518 [test_hmm]
>    | [<ffffffff02a3e026>] hmm_dmirror_exit+0x3e/0x1018 [test_hmm]
>    | [<ffffffff80102c14>] __riscv_sys_delete_module+0x15a/0x2a6
>    | [<ffffffff80fd020c>] do_trap_ecall_u+0x1f2/0x266
>    | [<ffffffff80fde0a2>] _new_vmalloc_restore_context_a0+0xc6/0xd2
>    | Code: bf51 7597 0184 8593 76a5 854a 4097 0029 80e7 2c00 (9002) 7597
>    | ---[ end trace 0000000000000000 ]---
>    | Kernel panic - not syncing: Fatal exception in interrupt
>
> Add a check to avoid calling the pmd dtor, if the calling context is
> vmemmap_free().
>
> Fixes: c75a74f4ba19 ("riscv: mm: Add memory hotplugging support")
> Signed-off-by: Björn Töpel <bjorn at rivosinc.com>
> ---
>   arch/riscv/mm/init.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 0e8c20adcd98..fc53ce748c80 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1566,7 +1566,7 @@ static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
>   	pmd_clear(pmd);
>   }
>   
> -static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> +static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud, bool is_vmemmap)
>   {
>   	struct page *page = pud_page(*pud);
>   	struct ptdesc *ptdesc = page_ptdesc(page);
> @@ -1579,7 +1579,8 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
>   			return;
>   	}
>   
> -	pagetable_pmd_dtor(ptdesc);
> +	if (!is_vmemmap)
> +		pagetable_pmd_dtor(ptdesc);
>   	if (PageReserved(page))
>   		free_reserved_page(page);
>   	else
> @@ -1703,7 +1704,7 @@ static void __meminit remove_pud_mapping(pud_t *pud_base, unsigned long addr, un
>   		remove_pmd_mapping(pmd_base, addr, next, is_vmemmap, altmap);
>   
>   		if (pgtable_l4_enabled)
> -			free_pmd_table(pmd_base, pudp);
> +			free_pmd_table(pmd_base, pudp, is_vmemmap);
>   	}
>   }
>   
>
> base-commit: 57f7c7dc78cd09622b12920d92b40c1ce11b234e


Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>

Thanks,

Alex