On 09/04/2020 11:23 PM, Gerald Schaefer wrote: > On Fri, 4 Sep 2020 18:01:15 +0200 > Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> wrote: > >> On Fri, 4 Sep 2020 17:26:47 +0200 >> Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> wrote: >> >>> On Fri, 4 Sep 2020 12:18:05 +0530 >>> Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote: >>> >>>> >>>> >>>> On 09/02/2020 05:12 PM, Aneesh Kumar K.V wrote: >>>>> This patch series includes fixes for debug_vm_pgtable test code so that >>>>> they follow page table updates rules correctly. The first two patches introduce >>>>> changes w.r.t ppc64. The patches are included in this series for completeness. We can >>>>> merge them via ppc64 tree if required. >>>>> >>>>> Hugetlb test is disabled on ppc64 because that needs larger change to satisfy >>>>> page table update rules. >>>>> >>>>> These tests are broken w.r.t page table update rules and results in kernel >>>>> crash as below. >>>>> >>>>> [ 21.083519] kernel BUG at arch/powerpc/mm/pgtable.c:304! >>>>> cpu 0x0: Vector: 700 (Program Check) at [c000000c6d1e76c0] >>>>> pc: c00000000009a5ec: assert_pte_locked+0x14c/0x380 >>>>> lr: c0000000005eeeec: pte_update+0x11c/0x190 >>>>> sp: c000000c6d1e7950 >>>>> msr: 8000000002029033 >>>>> current = 0xc000000c6d172c80 >>>>> paca = 0xc000000003ba0000 irqmask: 0x03 irq_happened: 0x01 >>>>> pid = 1, comm = swapper/0 >>>>> kernel BUG at arch/powerpc/mm/pgtable.c:304! >>>>> [link register ] c0000000005eeeec pte_update+0x11c/0x190 >>>>> [c000000c6d1e7950] 0000000000000001 (unreliable) >>>>> [c000000c6d1e79b0] c0000000005eee14 pte_update+0x44/0x190 >>>>> [c000000c6d1e7a10] c000000001a2ca9c pte_advanced_tests+0x160/0x3d8 >>>>> [c000000c6d1e7ab0] c000000001a2d4fc debug_vm_pgtable+0x7e8/0x1338 >>>>> [c000000c6d1e7ba0] c0000000000116ec do_one_initcall+0xac/0x5f0 >>>>> [c000000c6d1e7c80] c0000000019e4fac kernel_init_freeable+0x4dc/0x5a4 >>>>> [c000000c6d1e7db0] c000000000012474 kernel_init+0x24/0x160 >>>>> [c000000c6d1e7e20] c00000000000cbd0 ret_from_kernel_thread+0x5c/0x6c >>>>> >>>>> With DEBUG_VM disabled >>>>> >>>>> [ 20.530152] BUG: Kernel NULL pointer dereference on read at 0x00000000 >>>>> [ 20.530183] Faulting instruction address: 0xc0000000000df330 >>>>> cpu 0x33: Vector: 380 (Data SLB Access) at [c000000c6d19f700] >>>>> pc: c0000000000df330: memset+0x68/0x104 >>>>> lr: c00000000009f6d8: hash__pmdp_huge_get_and_clear+0xe8/0x1b0 >>>>> sp: c000000c6d19f990 >>>>> msr: 8000000002009033 >>>>> dar: 0 >>>>> current = 0xc000000c6d177480 >>>>> paca = 0xc00000001ec4f400 irqmask: 0x03 irq_happened: 0x01 >>>>> pid = 1, comm = swapper/0 >>>>> [link register ] c00000000009f6d8 hash__pmdp_huge_get_and_clear+0xe8/0x1b0 >>>>> [c000000c6d19f990] c00000000009f748 hash__pmdp_huge_get_and_clear+0x158/0x1b0 (unreliable) >>>>> [c000000c6d19fa10] c0000000019ebf30 pmd_advanced_tests+0x1f0/0x378 >>>>> [c000000c6d19fab0] c0000000019ed088 debug_vm_pgtable+0x79c/0x1244 >>>>> [c000000c6d19fba0] c0000000000116ec do_one_initcall+0xac/0x5f0 >>>>> [c000000c6d19fc80] c0000000019a4fac kernel_init_freeable+0x4dc/0x5a4 >>>>> [c000000c6d19fdb0] c000000000012474 kernel_init+0x24/0x160 >>>>> [c000000c6d19fe20] c00000000000cbd0 ret_from_kernel_thread+0x5c/0x6c >>>>> >>>>> Changes from v3: >>>>> * Address review feedback >>>>> * Move page table depost and withdraw patch after adding pmdlock to avoid bisect failure. >>>> >>>> This version >>>> >>>> - Builds on x86, arm64, s390, arc, powerpc and riscv (defconfig with DEBUG_VM_PGTABLE) >>>> - Runs on arm64 and x86 without any regression, atleast nothing that I have noticed >>>> - Will be great if this could get tested on s390, arc, riscv, ppc32 platforms as well >>> >>> When I quickly tested v3, it worked fine, but now it turned out to >>> only work fine "sometimes", both v3 and v4. I need to look into it >>> further, but so far it seems related to the hugetlb_advanced_tests(). >>> >>> I guess there was already some discussion on this test, but we did >>> not receive all of the thread(s). Please always add at least >>> linux-s390@xxxxxxxxxxxxxxx and maybe myself and Vasily Gorbik <gor@xxxxxxxxxxxxx> >>> for further discussions. >> >> BTW, with myself I mean the new address gerald.schaefer@xxxxxxxxxxxxx. >> The old gerald.schaefer@xxxxxxxxxx seems to work (again), but is not >> very reliable. >> >> BTW2, a quick test with this change (so far) made the issues on s390 >> go away: >> >> @@ -1069,7 +1074,7 @@ static int __init debug_vm_pgtable(void) >> spin_unlock(ptl); >> >> #ifndef CONFIG_PPC_BOOK3S_64 >> - hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot); >> + hugetlb_advanced_tests(mm, vma, (pte_t *) pmdp, pmd_aligned, vaddr, prot); >> #endif >> >> spin_lock(&mm->page_table_lock); >> >> That would more match the "pte_t pointer" usage for hugetlb code, >> i.e. just cast a pmd_t pointer to it. Also changed to pmd_aligned, >> but I think the root cause is the pte_t pointer. >> >> Not entirely sure though if that would really be the correct fix. >> I somehow lost whatever little track I had about what these tests >> really want to check, and if that would still be valid with that >> change. > > Another potential issue, apparently not for s390, but maybe for > others, is that the vaddr passed to hugetlb_advanced_tests() is > also not pmd/pud size aligned, like you did in pmd/pud_advanced_tests(). > > I guess for the hugetlb_advanced_tests() you need to choose if > you want to test pmd or pud hugepages, and accordingly prepare > the *ptep, pfn and vaddr input. If you only check for CONFIG_HUGETLB_PAGE, > then probably only pmd hugepages would be safe, there might be > architectures only supporting one hugepage size. I guess preparing for PMD based HugeTLB tests should be sufficient for now, which can be improved later on to cover other levels. > > So, for s390, at least the ptep input value is a problem. Still > need to better understand how it goes wrong, but it seems to be > fixed when using proper pmdp, and also works with pudp. > > For others, especially the apparent issues on ppc64, the other > non-hugepage aligned input pfn and vaddr might also be an issue, > e.g. power at least seems to use the vaddr in its set_huge_pte_at() > implementation for some pmd_off(mm, addr) calculation. > > Again, sorry if this was already discussed, I missed most of it > and honestly didn't properly look at the scarce mails that we did > receive... Sure, will consider these points and try improve tests afterwards.
