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 <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?
>
> 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.
