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 <aryabi...@virtuozzo.com>
>
> Reviewed-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
> Cc: sta...@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?
Thanks
Baoquan
>
> for (i = 0; i < PTRS_PER_P4D; i++) {
> p4d = p4d_offset(pgd,
> pgd_idx * PGDIR_SIZE + i * P4D_SIZE);
>
> - if (!(p4d_val(*p4d) & _PAGE_PRESENT))
> + if (!p4d_present(*p4d))
> continue;
>
> pud = (pud_t *)p4d_page_vaddr(*p4d);
> --
> Kirill A. Shutemov
