Re: [PATCH v2] x86/power/64: Support unaligned addresses for temporary mapping

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Saturday, August 06, 2016 09:53:50 PM Yinghai Lu wrote:
> On Sat, Aug 6, 2016 at 6:03 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > On Wednesday, August 03, 2016 11:28:48 PM Rafael J. Wysocki wrote:
> >
> > On a second thought, it seems to be better to follow your suggestion to simply
> > provide a special version of kernel_ident_mapping_init() for hibernation,
> > because it is sufficiently distinct from the other users of the code in
> > ident_map.c.
> >
> > The patch below does just that (lightly tested).
> >
> >
> > ---
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Subject: [PATCH] x86/power/64: Always create temporary identity mapping correctly
> >
> > The low-level resume-from-hibernation code on x86-64 uses
> > kernel_ident_mapping_init() to create the temoprary identity mapping,
> > but that function assumes that the offset between kernel virtual
> > addresses and physical addresses is aligned on the PGD level.
> >
> > However, with a randomized identity mapping base, it may be aligned
> > on the PUD level and if that happens, the temporary identity mapping
> > created by set_up_temporary_mappings() will not reflect the actual
> > kernel identity mapping and the image restoration will fail as a
> > result (leading to a kernel panic most of the time).
> >
> > To fix this problem, provide simplified routines for creating the
> > temporary identity mapping during resume from hibernation on x86-64
> > that support unaligned offsets between KVA and PA up to the PMD
> > level.
> >
> > Although kernel_ident_mapping_init() might be made work in that
> > case too, using hibernation-specific code for that is way simpler.
> >
> > Reported-by: Thomas Garnier <thgarnie@google.com>
> > Suggested-by: Yinghai Lu <yinghai@kernel.org>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  arch/x86/power/hibernate_64.c |   61 ++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 53 insertions(+), 8 deletions(-)
> >
> > Index: linux-pm/arch/x86/power/hibernate_64.c
> > ===================================================================
> > --- linux-pm.orig/arch/x86/power/hibernate_64.c
> > +++ linux-pm/arch/x86/power/hibernate_64.c
> > @@ -77,18 +77,63 @@ static int set_up_temporary_text_mapping
> >         return 0;
> >  }
> >
> > -static void *alloc_pgt_page(void *context)
> > +static void ident_pmd_init(pmd_t *pmd, unsigned long addr, unsigned long end)
> >  {
> > -       return (void *)get_safe_page(GFP_ATOMIC);
> > +       for (; addr < end; addr += PMD_SIZE)
> > +               set_pmd(pmd + pmd_index(addr),
> > +                       __pmd((addr - __PAGE_OFFSET) | __PAGE_KERNEL_LARGE_EXEC));
> > +}
> > +
> > +static int ident_pud_init(pud_t *pud, unsigned long addr, unsigned long end)
> > +{
> > +       unsigned long next;
> > +
> > +       for (; addr < end; addr = next) {
> > +               pmd_t *pmd;
> > +
> > +               pmd = (pmd_t *)get_safe_page(GFP_ATOMIC);
> > +               if (!pmd)
> > +                       return -ENOMEM;
> > +
> > +               next = (addr & PUD_MASK) + PUD_SIZE;
> > +               if (next > end)
> > +                       next = end;
> > +
> > +               ident_pmd_init(pmd, addr & PMD_MASK, next);
> > +               set_pud(pud + pud_index(addr), __pud(__pa(pmd) | _KERNPG_TABLE));
> > +       }
> > +       return 0;
> > +}
> > +
> > +static int ident_mapping_init(pgd_t *pgd, unsigned long mstart, unsigned long mend)
> > +{
> > +       unsigned long addr = mstart + __PAGE_OFFSET;
> > +       unsigned long end = mend + __PAGE_OFFSET;
> > +       unsigned long next;
> > +
> > +       for (; addr < end; addr = next) {
> > +               pud_t *pud;
> > +               int result;
> > +
> > +               pud = (pud_t *)get_safe_page(GFP_ATOMIC);
> > +               if (!pud)
> > +                       return -ENOMEM;
> > +
> > +               next = (addr & PGDIR_MASK) + PGDIR_SIZE;
> > +               if (next > end)
> > +                       next = end;
> > +
> > +               result = ident_pud_init(pud, addr, next);
> > +               if (result)
> > +                       return result;
> > +
> > +               set_pgd(pgd + pgd_index(addr), __pgd(__pa(pud) | _KERNPG_TABLE));
> > +       }
> > +       return 0;
> >  }
> >
> >  static int set_up_temporary_mappings(void)
> >  {
> > -       struct x86_mapping_info info = {
> > -               .alloc_pgt_page = alloc_pgt_page,
> > -               .pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
> > -               .kernel_mapping = true,
> > -       };
> >         unsigned long mstart, mend;
> >         pgd_t *pgd;
> >         int result;
> > @@ -108,7 +153,7 @@ static int set_up_temporary_mappings(voi
> >                 mstart = pfn_mapped[i].start << PAGE_SHIFT;
> >                 mend   = pfn_mapped[i].end << PAGE_SHIFT;
> >
> > -               result = kernel_ident_mapping_init(&info, pgd, mstart, mend);
> > +               result = ident_mapping_init(pgd, mstart, mend);
> >                 if (result)
> >                         return result;
> >         }
> >
> 
> Hi Rafael,
> 
> Your version seems not considering different pfn_mapped range could
> share same PGD (512G) or even PUD(1G), or even same PMD (2M) range.

Good point!

> so just keep on using kernel_ident_mapping_init() for that.

But then playing with offsets in ident_pud_init() is not necessary,
because that function works on virtual addresses only, so the appended patch
should be sufficient to fix the problem, shouldn't it?

> At the same time, set_up_temporary_text_mapping could be replaced with
> kernel_ident_mapping_init() too if restore_jump_address is KVA for
> jump_address_phys.

I see no reason to do that.

First, it is not guaranteed that restore_jump_address will always be a KVA for
jump_address_phys and second, it really is only necessary to map one PMD in
there.

Thanks,
Rafael


---
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH v2] x86/power/64: Always create temporary identity mapping correctly

The low-level resume-from-hibernation code on x86-64 uses
kernel_ident_mapping_init() to create the temoprary identity mapping,
but that function assumes that the offset between kernel virtual
addresses and physical addresses is aligned on the PGD level.

However, with a randomized identity mapping base, it may be aligned
on the PUD level and if that happens, the temporary identity mapping
created by set_up_temporary_mappings() will not reflect the actual
kernel identity mapping and the image restoration will fail as a
result (leading to a kernel panic most of the time).

To fix this problem, rework kernel_ident_mapping_init() to support
unaligned offsets between KVA and PA up to the PMD level and make
set_up_temporary_mappings() use it as approprtiate.

Reported-by: Thomas Garnier <thgarnie@google.com>
Suggested-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 arch/x86/include/asm/init.h   |    4 ++--
 arch/x86/mm/ident_map.c       |   19 +++++++++++--------
 arch/x86/power/hibernate_64.c |    2 +-
 3 files changed, 14 insertions(+), 11 deletions(-)

Index: linux-pm/arch/x86/include/asm/init.h
===================================================================
--- linux-pm.orig/arch/x86/include/asm/init.h
+++ linux-pm/arch/x86/include/asm/init.h
@@ -5,10 +5,10 @@ struct x86_mapping_info {
 	void *(*alloc_pgt_page)(void *); /* allocate buf for page table */
 	void *context;			 /* context for alloc_pgt_page */
 	unsigned long pmd_flag;		 /* page flag for PMD entry */
-	bool kernel_mapping;		 /* kernel mapping or ident mapping */
+	unsigned long offset;		 /* ident mapping offset */
 };
 
 int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
-				unsigned long addr, unsigned long end);
+				unsigned long pstart, unsigned long pend);
 
 #endif /* _ASM_X86_INIT_H */
Index: linux-pm/arch/x86/mm/ident_map.c
===================================================================
--- linux-pm.orig/arch/x86/mm/ident_map.c
+++ linux-pm/arch/x86/mm/ident_map.c
@@ -3,15 +3,17 @@
  * included by both the compressed kernel and the regular kernel.
  */
 
-static void ident_pmd_init(unsigned long pmd_flag, pmd_t *pmd_page,
+static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
 			   unsigned long addr, unsigned long end)
 {
 	addr &= PMD_MASK;
 	for (; addr < end; addr += PMD_SIZE) {
 		pmd_t *pmd = pmd_page + pmd_index(addr);
 
-		if (!pmd_present(*pmd))
-			set_pmd(pmd, __pmd(addr | pmd_flag));
+		if (pmd_present(*pmd))
+			continue;
+
+		set_pmd(pmd, __pmd((addr - info->offset) | info->pmd_flag));
 	}
 }
 
@@ -30,13 +32,13 @@ static int ident_pud_init(struct x86_map
 
 		if (pud_present(*pud)) {
 			pmd = pmd_offset(pud, 0);
-			ident_pmd_init(info->pmd_flag, pmd, addr, next);
+			ident_pmd_init(info, pmd, addr, next);
 			continue;
 		}
 		pmd = (pmd_t *)info->alloc_pgt_page(info->context);
 		if (!pmd)
 			return -ENOMEM;
-		ident_pmd_init(info->pmd_flag, pmd, addr, next);
+		ident_pmd_init(info, pmd, addr, next);
 		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
 	}
 
@@ -44,14 +46,15 @@ static int ident_pud_init(struct x86_map
 }
 
 int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
-			      unsigned long addr, unsigned long end)
+			      unsigned long pstart, unsigned long pend)
 {
+	unsigned long addr = pstart + info->offset;
+	unsigned long end = pend + info->offset;
 	unsigned long next;
 	int result;
-	int off = info->kernel_mapping ? pgd_index(__PAGE_OFFSET) : 0;
 
 	for (; addr < end; addr = next) {
-		pgd_t *pgd = pgd_page + pgd_index(addr) + off;
+		pgd_t *pgd = pgd_page + pgd_index(addr);
 		pud_t *pud;
 
 		next = (addr & PGDIR_MASK) + PGDIR_SIZE;
Index: linux-pm/arch/x86/power/hibernate_64.c
===================================================================
--- linux-pm.orig/arch/x86/power/hibernate_64.c
+++ linux-pm/arch/x86/power/hibernate_64.c
@@ -87,7 +87,7 @@ static int set_up_temporary_mappings(voi
 	struct x86_mapping_info info = {
 		.alloc_pgt_page	= alloc_pgt_page,
 		.pmd_flag	= __PAGE_KERNEL_LARGE_EXEC,
-		.kernel_mapping = true,
+		.offset		= __PAGE_OFFSET,
 	};
 	unsigned long mstart, mend;
 	pgd_t *pgd;