[PATCH 00/19] Add generic user_landing tracking

[PATCH 00/19] Add generic user_landing tracking

[Dmitry Safonov]

Started from discussion [1], where was noted that currently a couple of
architectures support mremap() for vdso/sigpage, but not munmap().
If an application maps something on the ex-place of vdso/sigpage,
later after processing signal it will land there (good luck!)

Patches set is based on linux-next (next-20201106) and it depends on
changes in x86/cleanups (those reclaim TIF_IA32/TIF_X32) and also
on my changes in akpm (fixing several mremap() issues).

Logically, the patches set divides on:
- patch       1: cleanup for patches in x86/cleanups
- patches  2-11: cleanups for arch_setup_additional_pages()
- patches 12-13: x86 signal changes for unmapped vdso
- patches 14-19: provide generic user_landing in mm_struct

In the end, besides cleanups, it's now more predictable what happens for
applications with unmapped vdso on architectures those support .mremap()
for vdso/sigpage.

I'm aware of only one user that unmaps vdso - Valgrind [2].
(there possibly are more, but this one is "special", it unmaps vdso, but
 not vvar, which confuses CRIU [Checkpoint Restore In Userspace], that's
 why I'm aware of it)

Patches as a .git branch:
https://github.com/0x7f454c46/linux/tree/setup_additional_pages

[1]: https://lore.kernel.org/linux-arch/CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com/
[2]: https://github.com/checkpoint-restore/criu/issues/488

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Guo Ren <guoren@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: x86@kernel.org

Dmitry Safonov (19):
  x86/elf: Check in_x32_syscall() in compat_arch_setup_additional_pages()
  elf: Move arch_setup_additional_pages() to generic elf.h
  arm64: Use in_compat_task() in arch_setup_additional_pages()
  x86: Remove compat_arch_setup_additional_pages()
  elf: Remove compat_arch_setup_additional_pages()
  elf/vdso: Reuse arch_setup_additional_pages() parameters
  elf: Use sysinfo_ehdr in ARCH_DLINFO()
  arm/vdso: Remove vdso pointer from mm->context
  s390/vdso: Remove vdso_base pointer from mm->context
  sparc/vdso: Remove vdso pointer from mm->context
  mm/mmap: Make vm_special_mapping::mremap return void
  x86/signal: Land on &frame->retcode when vdso isn't mapped
  x86/signal: Check if vdso_image_32 is mapped before trying to land on it
  mm: Add user_landing in mm_struct
  x86/vdso: Migrate to user_landing
  arm/vdso: Migrate to user_landing
  arm64/vdso: Migrate compat signals to user_landing
  arm64/vdso: Migrate native signals to user_landing
  mips/vdso: Migrate to user_landing

 arch/alpha/include/asm/elf.h              |  2 +-
 arch/arm/Kconfig                          |  2 +
 arch/arm/include/asm/elf.h                | 10 +---
 arch/arm/include/asm/mmu.h                |  3 -
 arch/arm/include/asm/vdso.h               |  6 +-
 arch/arm/kernel/process.c                 | 14 +----
 arch/arm/kernel/signal.c                  |  6 +-
 arch/arm/kernel/vdso.c                    | 20 ++-----
 arch/arm64/Kconfig                        |  2 +
 arch/arm64/include/asm/elf.h              | 27 ++-------
 arch/arm64/kernel/signal.c                | 10 +++-
 arch/arm64/kernel/signal32.c              | 17 ++++--
 arch/arm64/kernel/vdso.c                  | 47 ++++++---------
 arch/csky/Kconfig                         |  1 +
 arch/csky/include/asm/elf.h               |  4 --
 arch/csky/kernel/vdso.c                   |  3 +-
 arch/hexagon/Kconfig                      |  1 +
 arch/hexagon/include/asm/elf.h            |  6 --
 arch/hexagon/kernel/vdso.c                |  3 +-
 arch/ia64/include/asm/elf.h               |  2 +-
 arch/mips/Kconfig                         |  2 +
 arch/mips/include/asm/elf.h               | 10 +---
 arch/mips/kernel/signal.c                 | 11 ++--
 arch/mips/kernel/vdso.c                   |  5 +-
 arch/mips/vdso/genvdso.c                  |  9 ---
 arch/nds32/Kconfig                        |  1 +
 arch/nds32/include/asm/elf.h              |  8 +--
 arch/nds32/kernel/vdso.c                  |  3 +-
 arch/nios2/Kconfig                        |  1 +
 arch/nios2/include/asm/elf.h              |  4 --
 arch/nios2/mm/init.c                      |  2 +-
 arch/powerpc/Kconfig                      |  1 +
 arch/powerpc/include/asm/elf.h            |  9 +--
 arch/powerpc/kernel/vdso.c                |  3 +-
 arch/riscv/Kconfig                        |  1 +
 arch/riscv/include/asm/elf.h              | 10 +---
 arch/riscv/kernel/vdso.c                  |  9 +--
 arch/s390/Kconfig                         |  1 +
 arch/s390/include/asm/elf.h               | 10 +---
 arch/s390/include/asm/mmu.h               |  1 -
 arch/s390/kernel/vdso.c                   | 13 +---
 arch/sh/Kconfig                           |  1 +
 arch/sh/include/asm/elf.h                 | 16 ++---
 arch/sh/kernel/vsyscall/vsyscall.c        |  3 +-
 arch/sparc/Kconfig                        |  1 +
 arch/sparc/include/asm/elf_64.h           | 11 +---
 arch/sparc/include/asm/mmu_64.h           |  1 -
 arch/sparc/vdso/vma.c                     | 18 +++---
 arch/x86/Kconfig                          |  2 +
 arch/x86/entry/common.c                   |  8 ++-
 arch/x86/entry/vdso/vma.c                 | 72 ++++++++++++-----------
 arch/x86/ia32/ia32_signal.c               | 18 +++---
 arch/x86/include/asm/compat.h             |  6 ++
 arch/x86/include/asm/elf.h                | 44 +++++---------
 arch/x86/include/asm/mmu.h                |  1 -
 arch/x86/include/asm/vdso.h               |  4 ++
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  3 +-
 arch/x86/kernel/signal.c                  | 25 ++++----
 arch/x86/um/asm/elf.h                     |  9 +--
 arch/x86/um/vdso/vma.c                    |  2 +-
 fs/Kconfig.binfmt                         |  3 +
 fs/aio.c                                  |  3 +-
 fs/binfmt_elf.c                           | 19 +++---
 fs/binfmt_elf_fdpic.c                     | 17 +++---
 fs/compat_binfmt_elf.c                    | 12 ----
 include/linux/elf.h                       | 24 ++++++--
 include/linux/mm.h                        |  3 +-
 include/linux/mm_types.h                  | 12 +++-
 mm/Kconfig                                |  3 +
 mm/mmap.c                                 | 21 ++++++-
 mm/mremap.c                               |  2 +-
 71 files changed, 308 insertions(+), 356 deletions(-)


base-commit: c34f157421f6905e6b4a79a312e9175dce2bc607
-- 
2.28.0

[PATCH 14/19] mm: Add user_landing in mm_struct

[Dmitry Safonov]

Instead of having every architecture to define vdso_base/vdso_addr etc,
provide a generic mechanism to track landing in userspace.
It'll minimize per-architecture difference, the number of callbacks to
provide.

Originally, it started from thread [1] where the need for .close()
callback on vm_special_mapping was pointed, this generic code besides
removing duplicated .mremap() callbacks provides a cheaper way to
support munmap() on vdso mappings without introducing .close() callbacks
for every architecture (with would bring even more code duplication).

[1]: https://lore.kernel.org/linux-arch/CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com/
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  3 ++-
 fs/aio.c                                  |  3 ++-
 include/linux/mm.h                        |  3 ++-
 include/linux/mm_types.h                  | 10 ++++++++++
 mm/Kconfig                                |  3 +++
 mm/mmap.c                                 | 19 ++++++++++++++++++-
 mm/mremap.c                               |  2 +-
 7 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index e916646adc69..786c97203bf6 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1458,7 +1458,8 @@ static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-static int pseudo_lock_dev_mremap(struct vm_area_struct *area, unsigned long flags)
+static int pseudo_lock_dev_mremap(struct vm_area_struct *old_vma,
+		struct vm_area_struct *new_vma, unsigned long flags)
 {
 	/* Not supported */
 	return -EINVAL;
diff --git a/fs/aio.c b/fs/aio.c
index d1dad4cd860f..2695dc9ed46f 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -324,7 +324,8 @@ static void aio_free_ring(struct kioctx *ctx)
 	}
 }
 
-static int aio_ring_mremap(struct vm_area_struct *vma, unsigned long flags)
+static int aio_ring_mremap(struct vm_area_struct *old_vma,
+			   struct vm_area_struct *vma, unsigned long flags)
 {
 	struct file *file = vma->vm_file;
 	struct mm_struct *mm = vma->vm_mm;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 427911d2c83e..4b0f97a289b3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -559,7 +559,8 @@ struct vm_operations_struct {
 	void (*close)(struct vm_area_struct * area);
 	/* Called any time before splitting to check if it's allowed */
 	int (*may_split)(struct vm_area_struct *area, unsigned long addr);
-	int (*mremap)(struct vm_area_struct *area, unsigned long flags);
+	int (*mremap)(struct vm_area_struct *old_vma,
+			struct vm_area_struct *new_vma, unsigned long flags);
 	vm_fault_t (*fault)(struct vm_fault *vmf);
 	vm_fault_t (*huge_fault)(struct vm_fault *vmf,
 			enum page_entry_size pe_size);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b035caff6abe..f888257e973a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -488,6 +488,16 @@ struct mm_struct {
 
 		/* Architecture-specific MM context */
 		mm_context_t context;
+#ifdef CONFIG_ARCH_HAS_USER_LANDING
+		/*
+		 * Address of special mapping VMA to land after processing
+		 * a signal. Reads are unprotected: if a thread unmaps or
+		 * mremaps the mapping while another thread is processing
+		 * a signal, it can segfault while landing.
+		 */
+		void __user *user_landing;
+#endif
+#define UNMAPPED_USER_LANDING TASK_SIZE_MAX
 
 		unsigned long flags; /* Must use atomic bitops to access */
 
diff --git a/mm/Kconfig b/mm/Kconfig
index 01b0ae0cd9d3..d43b61a21be8 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -883,4 +883,7 @@ config ARCH_HAS_HUGEPD
 config MAPPING_DIRTY_HELPERS
         bool
 
+config ARCH_HAS_USER_LANDING
+	bool
+
 endmenu
diff --git a/mm/mmap.c b/mm/mmap.c
index 2376f3972f13..8a17ffdedacb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3410,11 +3410,25 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
 
 static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
 
+static void update_user_landing(struct vm_area_struct *old_vma,
+				unsigned long new_addr)
+{
+#ifdef CONFIG_ARCH_HAS_USER_LANDING
+	struct mm_struct *mm = old_vma->vm_mm;
+
+	if (WARN_ON_ONCE(!mm))
+		return;
+	if (old_vma->vm_start == (unsigned long)mm->user_landing)
+		mm->user_landing = (void __user *)new_addr;
+#endif
+}
+
 /*
  * Having a close hook prevents vma merging regardless of flags.
  */
 static void special_mapping_close(struct vm_area_struct *vma)
 {
+	update_user_landing(vma, UNMAPPED_USER_LANDING);
 }
 
 static const char *special_mapping_name(struct vm_area_struct *vma)
@@ -3422,7 +3436,8 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
 	return ((struct vm_special_mapping *)vma->vm_private_data)->name;
 }
 
-static int special_mapping_mremap(struct vm_area_struct *new_vma,
+static int special_mapping_mremap(struct vm_area_struct *old_vma,
+				  struct vm_area_struct *new_vma,
 				  unsigned long flags)
 {
 	struct vm_special_mapping *sm = new_vma->vm_private_data;
@@ -3436,6 +3451,8 @@ static int special_mapping_mremap(struct vm_area_struct *new_vma,
 	if (sm->mremap)
 		sm->mremap(sm, new_vma);
 
+	update_user_landing(old_vma, new_vma->vm_start);
+
 	return 0;
 }
 
diff --git a/mm/mremap.c b/mm/mremap.c
index c5590afe7165..9595f6b72101 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -543,7 +543,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	if (moved_len < old_len) {
 		err = -ENOMEM;
 	} else if (vma->vm_ops && vma->vm_ops->mremap) {
-		err = vma->vm_ops->mremap(new_vma, flags);
+		err = vma->vm_ops->mremap(vma, new_vma, flags);
 	}
 
 	if (unlikely(err)) {
-- 
2.28.0

[PATCH 19/19] mips/vdso: Migrate to user_landing

[Dmitry Safonov]

Generic way to track the land vma area.
As a bonus, after unmapping sigpage, kernel won't try to land on its
previous position.

Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 arch/mips/Kconfig         |  1 +
 arch/mips/kernel/signal.c | 11 +++++++----
 arch/mips/kernel/vdso.c   |  2 +-
 arch/mips/vdso/genvdso.c  |  8 --------
 4 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 5e696ab80df4..eedb1683ec8e 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -10,6 +10,7 @@ config MIPS
 	select ARCH_HAS_SETUP_ADDITIONAL_PAGES
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
+	select ARCH_HAS_USER_LANDING
 	select ARCH_SUPPORTS_UPROBES
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index f1e985109da0..eb79272d3cc2 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -806,11 +806,13 @@ struct mips_abi mips_abi = {
 
 static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
+	unsigned long land = (unsigned long)current->mm->user_landing;
 	sigset_t *oldset = sigmask_to_save();
-	int ret;
+	int ret = 1;
 	struct mips_abi *abi = current->thread.abi;
-	void *vdso = current->mm->context.vdso;
 
+	if (land == UNMAPPED_USER_LANDING)
+		goto err;
 	/*
 	 * If we were emulating a delay slot instruction, exit that frame such
 	 * that addresses in the sigframe are as expected for userland and we
@@ -843,12 +845,13 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 	rseq_signal_deliver(ksig, regs);
 
 	if (sig_uses_siginfo(&ksig->ka, abi))
-		ret = abi->setup_rt_frame(vdso + abi->vdso->off_rt_sigreturn,
+		ret = abi->setup_rt_frame(land + abi->vdso->off_rt_sigreturn,
 					  ksig, regs, oldset);
 	else
-		ret = abi->setup_frame(vdso + abi->vdso->off_sigreturn,
+		ret = abi->setup_frame(land + abi->vdso->off_sigreturn,
 				       ksig, regs, oldset);
 
+err:
 	signal_setup_done(ret, ksig, 0);
 }
 
diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
index a4a321252df6..5523ba25ab3d 100644
--- a/arch/mips/kernel/vdso.c
+++ b/arch/mips/kernel/vdso.c
@@ -183,7 +183,7 @@ int arch_setup_additional_pages(unsigned long *sysinfo_ehdr)
 		goto out;
 	}
 
-	mm->context.vdso = (void *)vdso_addr;
+	mm->user_landing = (void __user *)vdso_addr;
 	*sysinfo_ehdr = vdso_addr;
 	ret = 0;
 
diff --git a/arch/mips/vdso/genvdso.c b/arch/mips/vdso/genvdso.c
index 0303d30cde03..8f581a2c8578 100644
--- a/arch/mips/vdso/genvdso.c
+++ b/arch/mips/vdso/genvdso.c
@@ -259,13 +259,6 @@ int main(int argc, char **argv)
 	fprintf(out_file, "#include <linux/linkage.h>\n");
 	fprintf(out_file, "#include <linux/mm.h>\n");
 	fprintf(out_file, "#include <asm/vdso.h>\n");
-	fprintf(out_file, "static void vdso_mremap(\n");
-	fprintf(out_file, "	const struct vm_special_mapping *sm,\n");
-	fprintf(out_file, "	struct vm_area_struct *new_vma)\n");
-	fprintf(out_file, "{\n");
-	fprintf(out_file, "	current->mm->context.vdso =\n");
-	fprintf(out_file, "	(void *)(new_vma->vm_start);\n");
-	fprintf(out_file, "}\n");
 
 	/* Write out the stripped VDSO data. */
 	fprintf(out_file,
@@ -290,7 +283,6 @@ int main(int argc, char **argv)
 	fprintf(out_file, "\t.mapping = {\n");
 	fprintf(out_file, "\t\t.name = \"[vdso]\",\n");
 	fprintf(out_file, "\t\t.pages = vdso_pages,\n");
-	fprintf(out_file, "\t\t.mremap = vdso_mremap,\n");
 	fprintf(out_file, "\t},\n");
 
 	/* Calculate and write symbol offsets to <output file> */
-- 
2.28.0

Re: [PATCH 14/19] mm: Add user_landing in mm_struct

[Andy Lutomirski]

On Sat, Nov 7, 2020 at 9:18 PM Dmitry Safonov <dima@arista.com> wrote:
>
> Instead of having every architecture to define vdso_base/vdso_addr etc,
> provide a generic mechanism to track landing in userspace.
> It'll minimize per-architecture difference, the number of callbacks to
> provide.
>
> Originally, it started from thread [1] where the need for .close()
> callback on vm_special_mapping was pointed, this generic code besides
> removing duplicated .mremap() callbacks provides a cheaper way to
> support munmap() on vdso mappings without introducing .close() callbacks
> for every architecture (with would bring even more code duplication).

I find the naming odd.  It's called "user_landing", which is
presumably a hard-to-understand shorthand for "user mode landing pad
for return from a signal handler if SA_RESTORER is not set".  But,
looking at the actual code, it's not this at all -- it's just the vDSO
base address.

So how about just calling it vdso_base?  I'm very much in favor of
consolidating and cleaning up, and improving the vdso remap/unmap
code, but I'm not convinced that we should call it anything other than
the vdso base.

--Andy

Re: [PATCH 00/19] Add generic user_landing tracking

[Andy Lutomirski]

On Sat, Nov 7, 2020 at 9:17 PM Dmitry Safonov <dima@arista.com> wrote:
>
> Started from discussion [1], where was noted that currently a couple of
> architectures support mremap() for vdso/sigpage, but not munmap().
> If an application maps something on the ex-place of vdso/sigpage,
> later after processing signal it will land there (good luck!)
>
> Patches set is based on linux-next (next-20201106) and it depends on
> changes in x86/cleanups (those reclaim TIF_IA32/TIF_X32) and also
> on my changes in akpm (fixing several mremap() issues).
>
> Logically, the patches set divides on:
> - patch       1: cleanup for patches in x86/cleanups
> - patches  2-11: cleanups for arch_setup_additional_pages()

I like these cleanups, although I think you should stop using terms
like "new-born".  A task being exec'd is not newborn at all -- it's in
the middle of a transformation.

--Andy

Re: [PATCH 14/19] mm: Add user_landing in mm_struct

[Dmitry Safonov]

On 11/8/20 7:04 PM, Andy Lutomirski wrote:
> On Sat, Nov 7, 2020 at 9:18 PM Dmitry Safonov <dima@arista.com> wrote:
>>
>> Instead of having every architecture to define vdso_base/vdso_addr etc,
>> provide a generic mechanism to track landing in userspace.
>> It'll minimize per-architecture difference, the number of callbacks to
>> provide.
>>
>> Originally, it started from thread [1] where the need for .close()
>> callback on vm_special_mapping was pointed, this generic code besides
>> removing duplicated .mremap() callbacks provides a cheaper way to
>> support munmap() on vdso mappings without introducing .close() callbacks
>> for every architecture (with would bring even more code duplication).
> 
> I find the naming odd.  It's called "user_landing", which is
> presumably a hard-to-understand shorthand for "user mode landing pad
> for return from a signal handler if SA_RESTORER is not set".  But,
> looking at the actual code, it's not this at all -- it's just the vDSO
> base address.

Agree. Originally, I tried to track the actual landing address on the
vdso, but .mremap() seemed simpler when tracking the vma base.

> So how about just calling it vdso_base?  I'm very much in favor of
> consolidating and cleaning up, and improving the vdso remap/unmap
> code, but I'm not convinced that we should call it anything other than
> the vdso base.

Sure.

Thanks,
         Dmitry

Re: [PATCH 00/19] Add generic user_landing tracking

[Dmitry Safonov]

On 11/8/20 7:07 PM, Andy Lutomirski wrote:
> On Sat, Nov 7, 2020 at 9:17 PM Dmitry Safonov <dima@arista.com> wrote:
>>
>> Started from discussion [1], where was noted that currently a couple of
>> architectures support mremap() for vdso/sigpage, but not munmap().
>> If an application maps something on the ex-place of vdso/sigpage,
>> later after processing signal it will land there (good luck!)
>>
>> Patches set is based on linux-next (next-20201106) and it depends on
>> changes in x86/cleanups (those reclaim TIF_IA32/TIF_X32) and also
>> on my changes in akpm (fixing several mremap() issues).
>>
>> Logically, the patches set divides on:
>> - patch       1: cleanup for patches in x86/cleanups
>> - patches  2-11: cleanups for arch_setup_additional_pages()
> 
> I like these cleanups, although I think you should stop using terms
> like "new-born".  A task being exec'd is not newborn at all -- it's in
> the middle of a transformation.

Thank you for looking at them, Andy :-)

Yeah, somehow I thought about new-execed process as a new-born binary.
I'll try to improve changelogs in v2.

Thanks,
         Dmitry