Le 26/03/2021 à 20:17, Dmitry Safonov a écrit :
Since commit 511157ab641e ("powerpc/vdso: Move vdso datapage up front")
VVAR page is in front of the VDSO area. In result it breaks CRIU
(Checkpoint Restore In Userspace) [1], where CRIU expects that "[vdso]"
from /proc/../maps points at ELF/vdso image, rather than at VVAR data page.
Laurent made a patch to keep CRIU working (by reading aux vector).
But I think it still makes sence to separate two mappings into different
VMAs. It will also make ppc64 less "special" for userspace and as
a side-bonus will make VVAR page un-writable by debugger (which previously
would COW page and can be unexpected).
I opportunistically Cc stable on it: I understand that usually such
stuff isn't a stable material, but that will allow us in CRIU have
one workaround less that is needed just for one release (v5.11) on
one platform (ppc64), which we otherwise have to maintain.
I wouldn't go as far as to say that the commit 511157ab641e is ABI
regression as no other userspace got broken, but I'd really appreciate
if it gets backported to v5.11 after v5.12 is released, so as not
to complicate already non-simple CRIU-vdso code. Thanks!
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # v5.11
[1]: https://github.com/checkpoint-restore/criu/issues/1417
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
Tested-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/include/asm/mmu_context.h | 2 +-
arch/powerpc/kernel/vdso.c | 54 +++++++++++++++++++-------
2 files changed, 40 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 652ce85f9410..4bc45d3ed8b0 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -263,7 +263,7 @@ extern void arch_exit_mmap(struct mm_struct *mm);
static inline void arch_unmap(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
- unsigned long vdso_base = (unsigned long)mm->context.vdso - PAGE_SIZE;
+ unsigned long vdso_base = (unsigned long)mm->context.vdso;
if (start <= vdso_base && vdso_base < end)
mm->context.vdso = NULL;
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index e839a906fdf2..b14907209822 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -55,10 +55,10 @@ static int vdso_mremap(const struct vm_special_mapping *sm, struct vm_area_struc
{
unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
- if (new_size != text_size + PAGE_SIZE)
+ if (new_size != text_size)
return -EINVAL;
In ARM64 you have removed the above test in commit 871402e05b24cb56 ("mm: forbid splitting special
mappings"). Do we need to keep it here ?
- current->mm->context.vdso = (void __user *)new_vma->vm_start + PAGE_SIZE;
+ current->mm->context.vdso = (void __user *)new_vma->vm_start;
return 0;
}
