On 17/01/2024 17:10, Breno Leitao wrote: > Currently there is a bug that a huge page could be stolen, and when the > original owner tries to fault in it, it causes a page fault. > > You can achieve that by: > 1) Creating a single page > echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages > > 2) mmap() the page above with MAP_HUGETLB into (void *ptr1). > * This will mark the page as reserved > 3) touch the page, which causes a page fault and allocates the page > * This will move the page out of the free list. > * It will also unreserved the page, since there is no more free > page > 4) madvise(MADV_DONTNEED) the page > * This will free the page, but not mark it as reserved. > 5) Allocate a secondary page with mmap(MAP_HUGETLB) into (void *ptr2). > * it should fail, but, since there is no more available page. > * But, since the page above is not reserved, this mmap() succeed. > 6) Faulting at ptr1 will cause a SIGBUS > * it will try to allocate a huge page, but there is none > available > > A full reproducer is in selftest. See > https://lore.kernel.org/all/20240105155419.1939484-1-leitao@xxxxxxxxxx/ > > Fix this by restoring the reserved page if necessary. If the page being > unmapped has HPAGE_RESV_OWNER set, and needs a reservation, set the > restore_reserve flag, which will move the page from free to reserved. > > Suggested-by: Rik van Riel <riel@xxxxxxxxxxx> > Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx> > --- > mm/hugetlb.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index ed1581b670d4..fa2c17767e44 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5677,6 +5677,16 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, > hugetlb_count_sub(pages_per_huge_page(h), mm); > hugetlb_remove_rmap(page_folio(page)); > > + if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && > + vma_needs_reservation(h, vma, start)) { > + /* > + * Restore the reservation if needed, otherwise the > + * backing page could be stolen by someone. > + */ > + folio_set_hugetlb_restore_reserve(page_folio(page)); > + vma_add_reservation(h, vma, address); > + } > + > spin_unlock(ptl); > tlb_remove_page_size(tlb, page, huge_page_size(h)); > /* Hi Breno, I'm seeing a kernel bug fire when running the "map_hugetlb" mm selftest against latest mm-unstable. Bisect tells me this patch is culprit. I'm running on arm64 with defconfig plus the following: # Woraround mm-unstable build errors. ./scripts/config --file ${param:builddir}/.config --enable ANON_VMA_NAME # Squashfs for snaps, xfs for large file folios. ./scripts/config --enable CONFIG_SQUASHFS_LZ4 ./scripts/config --enable CONFIG_SQUASHFS_LZO ./scripts/config --enable CONFIG_SQUASHFS_XZ ./scripts/config --enable CONFIG_SQUASHFS_ZSTD ./scripts/config --enable CONFIG_XFS_FS # Useful trace features (on for Ubuntu configs). ./scripts/config --enable CONFIG_FTRACE ./scripts/config --enable CONFIG_FUNCTION_TRACER ./scripts/config --enable CONFIG_KPROBES ./scripts/config --enable CONFIG_HIST_TRIGGERS ./scripts/config --enable CONFIG_FTRACE_SYSCALLS # For general mm debug. ./scripts/config --enable CONFIG_DEBUG_VM ./scripts/config --enable CONFIG_DEBUG_VM_MAPLE_TREE ./scripts/config --enable CONFIG_DEBUG_VM_RB ./scripts/config --enable CONFIG_DEBUG_VM_PGFLAGS ./scripts/config --enable CONFIG_DEBUG_VM_PGTABLE ./scripts/config --enable CONFIG_PAGE_TABLE_CHECK # For mm selftests. ./scripts/config --enable CONFIG_USERFAULTFD ./scripts/config --enable CONFIG_TEST_VMALLOC ./scripts/config --enable CONFIG_GUP_TEST Steps to reproduce: $ sudo ./map_hugetlb git bisect log: git bisect start # good: [6613476e225e090cc9aad49be7fa504e290dd33d] Linux 6.8-rc1 git bisect good 6613476e225e090cc9aad49be7fa504e290dd33d # bad: [ba34798948c09778ff707415fd52daa591bd361a] mm: add swappiness= arg to memory.reclaim git bisect bad ba34798948c09778ff707415fd52daa591bd361a # bad: [69d0e75874638fe852ed7004666e068cf9e2148d] mm: list_lru: disable memcg_aware when cgroup.memory is set to "nokmem" git bisect bad 69d0e75874638fe852ed7004666e068cf9e2148d # good: [38c61fca93058635b533ad927c1d6529757424d3] mm: huge_memory: don't force huge page alignment on 32 bit git bisect good 38c61fca93058635b533ad927c1d6529757424d3 # bad: [552225e31fdc31315d06c5c7f59b8dbc78e45d18] mm: vmalloc: rename adjust_va_to_fit_type() function git bisect bad 552225e31fdc31315d06c5c7f59b8dbc78e45d18 # bad: [184c8db9112ee2370c2d17efab76a6c2aad061bc] s390/sclp: remove unhandled memory notifier type git bisect bad 184c8db9112ee2370c2d17efab76a6c2aad061bc # bad: [7ccaa21733f6a0fefdf978da0ee08a459c8441ca] mm/cma: fix placement of trace_cma_alloc_start/finish git bisect bad 7ccaa21733f6a0fefdf978da0ee08a459c8441ca # bad: [be7a8289b10f82365b9a209d9db9e4aaab1a86d4] selftests/mm: run_vmtests.sh: add hugetlb_madv_vs_map git bisect bad be7a8289b10f82365b9a209d9db9e4aaab1a86d4 # bad: [947b031634e7af3d265275c26ec17e2f96fdb5a1] mm/hugetlb: restore the reservation if needed git bisect bad 947b031634e7af3d265275c26ec17e2f96fdb5a1 # first bad commit: [947b031634e7af3d265275c26ec17e2f96fdb5a1] mm/hugetlb: restore the reservation if needed BUG: [ 11.959447] kernel BUG at mm/hugetlb.c:1129! [ 11.959628] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [ 11.959870] Modules linked in: [ 11.959975] CPU: 0 PID: 1211 Comm: map_hugetlb Not tainted 6.8.0-rc1-00029-g947b031634e7 #11 [ 11.960272] Hardware name: linux,dummy-virt (DT) [ 11.960434] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 11.960680] pc : resv_map_release+0xa8/0xb8 [ 11.960895] lr : resv_map_release+0x6c/0xb8 [ 11.961041] sp : ffff80008863bb20 [ 11.961159] x29: ffff80008863bb20 x28: 0000000000000000 x27: 0000000000000001 [ 11.961500] x26: ffff77b80e91a704 x25: 0000000000000001 x24: ffff77b80e91a708 [ 11.961740] x23: ffff77b80e91a700 x22: 0000000000000080 x21: 0000000000000000 [ 11.961992] x20: ffff77b80e91a720 x19: ffff77b80e91a720 x18: 0000fffff7fecfff [ 11.962239] x17: 0000000000000000 x16: 1fffeef701697601 x15: 0000000000000001 [ 11.962484] x14: ffffffffffffffff x13: 0000000000000000 x12: ffffc8c6bc3b3cd0 [ 11.962729] x11: 0000000000000001 x10: 0000000000000000 x9 : ffffc8c6bad5245c [ 11.962971] x8 : ffff80008863bae0 x7 : 0000000000000000 x6 : ffff77b801966900 [ 11.963285] x5 : ffffc8c6bad6b7e4 x4 : fffffddee1613ea0 x3 : 0000000000400010 [ 11.963629] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 000000000000007f [ 11.963945] Call trace: [ 11.964070] resv_map_release+0xa8/0xb8 [ 11.964255] hugetlb_vm_op_close+0x1a0/0x1f0 [ 11.964431] remove_vma+0x34/0x88 [ 11.964604] do_vmi_align_munmap+0x4b8/0x5f0 [ 11.964792] do_vmi_munmap+0xb4/0x138 [ 11.964936] __vm_munmap+0xa8/0x188 [ 11.965074] __arm64_sys_munmap+0x28/0x40 [ 11.965237] invoke_syscall+0x50/0x128 [ 11.965388] el0_svc_common.constprop.0+0x48/0xf0 [ 11.965573] do_el0_svc+0x24/0x38 [ 11.965705] el0_svc+0x34/0xb8 [ 11.965862] el0t_64_sync_handler+0x100/0x130 [ 11.966032] el0t_64_sync+0x190/0x198 [ 11.966174] Code: a8c47bfd d50323bf d65f03c0 a9025bf5 (d4210000) [ 11.966410] ---[ end trace 0000000000000000 ]--- [ 11.966594] note: map_hugetlb[1211] exited with irqs disabled [ 11.966874] note: map_hugetlb[1211] exited with preempt_count 1 [ 11.967915] ------------[ cut here ]------------ [ 11.968165] WARNING: CPU: 0 PID: 0 at kernel/context_tracking.c:128 ct_kernel_exit.constprop.0+0x108/0x120 [ 11.968560] Modules linked in: [ 11.968651] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G D 6.8.0-rc1-00029-g947b031634e7 #11 [ 11.969235] Hardware name: linux,dummy-virt (DT) [ 11.970045] pstate: 214003c5 (nzCv DAIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 11.970941] pc : ct_kernel_exit.constprop.0+0x108/0x120 [ 11.971241] lr : ct_idle_enter+0x10/0x20 [ 11.971397] sp : ffffc8c6bd7f3d40 [ 11.971527] x29: ffffc8c6bd7f3d40 x28: 000000004224d0ac x27: 0000000000000000 [ 11.971811] x26: 0000000000000000 x25: ffffc8c6bd804980 x24: 0000000000000000 [ 11.972279] x23: 0000000000000000 x22: ffffc8c6bd804980 x21: ffffc8c6bd7f9ae0 [ 11.973023] x20: ffffc8c6bd7f9a20 x19: ffff77b83ff8dce0 x18: 0000000000000001 [ 11.973856] x17: 0000000000000000 x16: 1fffeef701697721 x15: 0000fffff7fed000 [ 11.975799] x14: ffff80008863b688 x13: 0000000000000000 x12: ffffc8c6bc3b3cd0 [ 11.976202] x11: 0000000000000001 x10: fc206bc54f751bff x9 : ffffc8c6bab7f564 [ 11.976461] x8 : ffffc8c6bd805a58 x7 : 00000000000001e5 x6 : 00000000119b8986 [ 11.976722] x5 : 4000000000000002 x4 : ffffaef18328b000 x3 : ffffc8c6bd7f3d40 [ 11.976985] x2 : ffffc8c6bcd02ce0 x1 : 4000000000000000 x0 : ffffc8c6bcd02ce0 [ 11.977245] Call trace: [ 11.977338] ct_kernel_exit.constprop.0+0x108/0x120 [ 11.977520] ct_idle_enter+0x10/0x20 [ 11.977654] default_idle_call+0x3c/0x170 [ 11.977804] do_idle+0x218/0x278 [ 11.977942] cpu_startup_entry+0x40/0x50 [ 11.978087] rest_init+0xf0/0xf8 [ 11.978209] arch_call_rest_init+0x18/0x20 [ 11.978391] start_kernel+0x524/0x670 [ 11.978528] __primary_switched+0xb8/0xc8 [ 11.978681] ---[ end trace 0000000000000000 ]--- Thanks, Ryan
