Messages in this thread | | | Date | Wed, 27 Jun 2018 07:08:17 +0800 | From | Baoquan He <> | Subject | Re: [PATCH] x86/mm: don't free p4d table when it is folded at runtime. |
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On 06/26/18 at 01:00pm, Kirill A. Shutemov wrote: > On Tue, Jun 26, 2018 at 07:40:49AM +0000, Baoquan He wrote: > > Hi Kirill, > > > > On 06/25/18 at 02:50pm, Kirill A. Shutemov wrote: > > > On Mon, Jun 25, 2018 at 01:24:27PM +0300, Andrey Ryabinin wrote: > > > > When the p4d page table layer is folded at runtime, the p4d_free() > > > > should do nothing, the same as in <asm-generic/pgtable-nop4d.h>. > > > > > > > > It seems this bug should cause double-free in efi_call_phys_epilog(), > > > > but I don't know how to trigger that code path, so I can't confirm that > > > > by testing. > > > > > > + Baoquan, Matt. > > > > > > There's other bug in the efi_call_phys_epilog() that prevents the bug from > > > being triggered. > > > > > > With the patch below. You can trigger the bug with efi=old_map in kernel > > > command line + KALSR and CONFIG_X86_5LEVEL=y: > > > > > > page:fffff6bec0000000 count:0 mapcount:1 mapping:0000000000000000 index:0x0 > > > flags: 0x800(reserved) > > > raw: 0000000000000800 fffff6bec0000008 fffff6bec0000008 0000000000000000 > > > raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) > > > ------------[ cut here ]------------ > > > kernel BUG at /home/kas/linux/la57/include/linux/mm.h:499! > > > invalid opcode: 0000 [#1] PREEMPT SMP > > > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.18.0-rc2-00037-g6f0d349d922b-dirty #58 > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 > > > RIP: 0010:__free_pages+0x28/0x30 > > > Code: 00 00 8b 47 34 85 c0 74 15 f0 ff 4f 34 75 09 85 f6 74 06 e9 ca d8 ff ff c3 e9 64 ff ff ff 48 > > > RSP: 0000:ffffffff9a403e90 EFLAGS: 00000246 > > > RAX: 000000000000003e RBX: ffffffff9a41d000 RCX: 0000000000000002 > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000ffffffff > > > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > > > R10: 0000000000000000 R11: 0000000000000000 R12: ffff9092af089000 > > > R13: ffffffff9a598a80 R14: 0000000000000001 R15: 0000000000000001 > > > FS: 0000000000000000(0000) GS:ffff9092bfc00000(0000) knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: ffff9092bffff000 CR3: 0000000198e1d000 CR4: 00000000000006b0 > > > Call Trace: > > > efi_call_phys_epilog+0x17d/0x1bb > > > efi_enter_virtual_mode+0x457/0x4ca > > > start_kernel+0x443/0x4dc > > > secondary_startup_64+0xb7/0xc0 > > > Modules linked in: > > > ---[ end trace 61e271260b11acdd ]--- > > > > > > I'll send patch for efi_call_phys_epilog(). > > > > > > > > > > > Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime") > > > > Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > > > > > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > > Cc: stable@vger.kernel.org # 4.17 > > > > > > > --- > > > > arch/x86/include/asm/pgalloc.h | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h > > > > index ada6410fd2ec..fbd578daa66e 100644 > > > > --- a/arch/x86/include/asm/pgalloc.h > > > > +++ b/arch/x86/include/asm/pgalloc.h > > > > @@ -184,6 +184,9 @@ static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr) > > > > > > > > static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d) > > > > { > > > > + if (!pgtable_l5_enabled()) > > > > + return; > > > > + > > > > BUG_ON((unsigned long)p4d & (PAGE_SIZE-1)); > > > > free_page((unsigned long)p4d); > > > > } > > > > > > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c > > > index e01f7ceb9e7a..77873ce700ae 100644 > > > --- a/arch/x86/platform/efi/efi_64.c > > > +++ b/arch/x86/platform/efi/efi_64.c > > > @@ -166,14 +166,14 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd) > > > pgd = pgd_offset_k(pgd_idx * PGDIR_SIZE); > > > set_pgd(pgd_offset_k(pgd_idx * PGDIR_SIZE), save_pgd[pgd_idx]); > > > > > > - if (!(pgd_val(*pgd) & _PAGE_PRESENT)) > > > + if (!pgd_present(*pgd)) > > > continue; > > > > I may not understand boot-time p4d folding. Here p4d is folded, why > > pgd_present() need always return 1 if p4d folded? > > Yeah. This is confusing. Basically, we pretend that p4d level consist of 1 > entry, with the same value as pgd above. We say that pgd is always present > and all checks happens on p4d level. > > It's not specific to boot-time folding. Compilet-time folding doing the > same. See include/asm-generic/pgtable-nop4d.h (and the rest -nop?d.h)
Thanks for telling, Kirill. Then the next p4d_present will do the real _PAGE_PRESENT checking. If so, I think this is a good fix.
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