[PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Mark Salter]

The arm64 linker script doesn't use the PAGE_ALIGNED_DATA macro which
leads to a ".data..page_aligned" section being placed between the end
of .data and start of .bss:

 % readelf -e vmlinux
   ...
 Section to Segment mapping:
  Segment Sections...
   00     .head.text .text .text.init .rodata __ksymtab __ksymtab_gpl \
          __ksymtab_strings __param __modver __ex_table .notes \
          .init.text .init.data .data..percpu .data .data..page_aligned .bss

This causes problems for the EFI stub which may have to relocate the
kernel image based on stext and _edata symbols.

This patch adds PAGE_ALIGNED_DATA() to the linker script inside the
the .data section.

Signed-off-by: Mark Salter <msalter@redhat.com>
---
 arch/arm64/kernel/vmlinux.lds.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index f8ab9d8..e441556 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -110,6 +110,7 @@ SECTIONS
 		 */
 		INIT_TASK_DATA(THREAD_SIZE)
 		NOSAVE_DATA
+		PAGE_ALIGNED_DATA(PAGE_SIZE)
 		CACHELINE_ALIGNED_DATA(64)
 		READ_MOSTLY_DATA(64)
 
-- 
1.8.3.1

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Will Deacon]

On Tue, Oct 08, 2013 at 09:37:39PM +0100, Mark Salter wrote:
> The arm64 linker script doesn't use the PAGE_ALIGNED_DATA macro which
> leads to a ".data..page_aligned" section being placed between the end
> of .data and start of .bss:
> 
>  % readelf -e vmlinux
>    ...
>  Section to Segment mapping:
>   Segment Sections...
>    00     .head.text .text .text.init .rodata __ksymtab __ksymtab_gpl \
>           __ksymtab_strings __param __modver __ex_table .notes \
>           .init.text .init.data .data..percpu .data .data..page_aligned .bss
> 
> This causes problems for the EFI stub which may have to relocate the
> kernel image based on stext and _edata symbols.
> 
> This patch adds PAGE_ALIGNED_DATA() to the linker script inside the
> the .data section.
> 
> Signed-off-by: Mark Salter <msalter@redhat.com>
> ---
>  arch/arm64/kernel/vmlinux.lds.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index f8ab9d8..e441556 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -110,6 +110,7 @@ SECTIONS
>  		 */
>  		INIT_TASK_DATA(THREAD_SIZE)
>  		NOSAVE_DATA
> +		PAGE_ALIGNED_DATA(PAGE_SIZE)
>  		CACHELINE_ALIGNED_DATA(64)
>  		READ_MOSTLY_DATA(64)

Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
THREAD_SIZE) instead?

Will

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Mark Salter]

On Wed, 2013-10-09 at 11:14 +0100, Will Deacon wrote:
> On Tue, Oct 08, 2013 at 09:37:39PM +0100, Mark Salter wrote:
> > The arm64 linker script doesn't use the PAGE_ALIGNED_DATA macro which
> > leads to a ".data..page_aligned" section being placed between the end
> > of .data and start of .bss:
> > 
> >  % readelf -e vmlinux
> >    ...
> >  Section to Segment mapping:
> >   Segment Sections...
> >    00     .head.text .text .text.init .rodata __ksymtab __ksymtab_gpl \
> >           __ksymtab_strings __param __modver __ex_table .notes \
> >           .init.text .init.data .data..percpu .data .data..page_aligned .bss
> > 
> > This causes problems for the EFI stub which may have to relocate the
> > kernel image based on stext and _edata symbols.
> > 
> > This patch adds PAGE_ALIGNED_DATA() to the linker script inside the
> > the .data section.
> > 
> > Signed-off-by: Mark Salter <msalter@redhat.com>
> > ---
> >  arch/arm64/kernel/vmlinux.lds.S | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> > index f8ab9d8..e441556 100644
> > --- a/arch/arm64/kernel/vmlinux.lds.S
> > +++ b/arch/arm64/kernel/vmlinux.lds.S
> > @@ -110,6 +110,7 @@ SECTIONS
> >  		 */
> >  		INIT_TASK_DATA(THREAD_SIZE)
> >  		NOSAVE_DATA
> > +		PAGE_ALIGNED_DATA(PAGE_SIZE)
> >  		CACHELINE_ALIGNED_DATA(64)
> >  		READ_MOSTLY_DATA(64)
> 
> Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
> THREAD_SIZE) instead?

Possibly. The layout of the included macros is the same. The only
difference being the placement of _data, _sdata, and _edata inside
.data and the use of __data_loc.

--Mark

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Mark Salter]

On Wed, 2013-10-09 at 11:14 +0100, Will Deacon wrote:
> > @@ -110,6 +110,7 @@ SECTIONS
> >                */
> >               INIT_TASK_DATA(THREAD_SIZE)
> >               NOSAVE_DATA
> > +             PAGE_ALIGNED_DATA(PAGE_SIZE)
> >               CACHELINE_ALIGNED_DATA(64)
> >               READ_MOSTLY_DATA(64)
> 
> Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
> THREAD_SIZE) instead?
> 

I took a look at this. It can be done, but the RW_DATA_SECTION aligns
data to PAGE_SIZE where the existing alignment is THREAD_SIZE. So using
RW_DATA_SECTION would waste some space if using 64K pagesize.

--Mark

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Mark Salter]

On Fri, 2013-10-11 at 08:18 -0400, Mark Salter wrote:
> On Wed, 2013-10-09 at 11:14 +0100, Will Deacon wrote:
> > > @@ -110,6 +110,7 @@ SECTIONS
> > >                */
> > >               INIT_TASK_DATA(THREAD_SIZE)
> > >               NOSAVE_DATA
> > > +             PAGE_ALIGNED_DATA(PAGE_SIZE)
> > >               CACHELINE_ALIGNED_DATA(64)
> > >               READ_MOSTLY_DATA(64)
> > 
> > Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
> > THREAD_SIZE) instead?
> > 
> 
> I took a look at this. It can be done, but the RW_DATA_SECTION aligns
> data to PAGE_SIZE where the existing alignment is THREAD_SIZE. So using
> RW_DATA_SECTION would waste some space if using 64K pagesize.
> 
> --Mark

So where do we stand with this one?

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Will Deacon]

On Fri, Nov 01, 2013 at 03:01:30PM +0000, Mark Salter wrote:
> On Fri, 2013-10-11 at 08:18 -0400, Mark Salter wrote:
> > On Wed, 2013-10-09 at 11:14 +0100, Will Deacon wrote:
> > > > @@ -110,6 +110,7 @@ SECTIONS
> > > >                */
> > > >               INIT_TASK_DATA(THREAD_SIZE)
> > > >               NOSAVE_DATA
> > > > +             PAGE_ALIGNED_DATA(PAGE_SIZE)
> > > >               CACHELINE_ALIGNED_DATA(64)
> > > >               READ_MOSTLY_DATA(64)
> > > 
> > > Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
> > > THREAD_SIZE) instead?
> > > 
> > 
> > I took a look at this. It can be done, but the RW_DATA_SECTION aligns
> > data to PAGE_SIZE where the existing alignment is THREAD_SIZE. So using
> > RW_DATA_SECTION would waste some space if using 64K pagesize.
> > 
> > --Mark
> 
> So where do we stand with this one?

I'd probably go for using the generic macro, but I don't have strong
preferences either way.

Will

Re: [PATCH] arm64: add PAGE_ALIGNED_DATA to linker script

[Catalin Marinas]

On Fri, Oct 11, 2013 at 01:18:41PM +0100, Mark Salter wrote:
> On Wed, 2013-10-09 at 11:14 +0100, Will Deacon wrote:
> > > @@ -110,6 +110,7 @@ SECTIONS
> > >                */
> > >               INIT_TASK_DATA(THREAD_SIZE)
> > >               NOSAVE_DATA
> > > +             PAGE_ALIGNED_DATA(PAGE_SIZE)
> > >               CACHELINE_ALIGNED_DATA(64)
> > >               READ_MOSTLY_DATA(64)
> > 
> > Can we just replace this chunk with RW_DATA_SECTION(64, PAGE_SIZE,
> > THREAD_SIZE) instead?
> > 
> 
> I took a look at this. It can be done, but the RW_DATA_SECTION aligns
> data to PAGE_SIZE where the existing alignment is THREAD_SIZE. So using
> RW_DATA_SECTION would waste some space if using 64K pagesize.

I think that's ok, especially since we may get security patches in the
future to create more restrictive page table attributes (well, with the
drawback of more TLB pressure). So I'm for more cleanup in the vmlinux
file by using the generic defines.

-- 
Catalin

[PATCH] arm64: use generic RW_DATA_SECTION macro in linker script

[Mark Salter]

The .data section in the arm64 linker script currently lacks a
definition for page-aligned data. This leads to a .page_aligned
section being placed between the end of data and start of bss.
This patch corrects that by using the generic RW_DATA_SECTION
macro which includes support for page-aligned data.

Signed-off-by: Mark Salter <msalter@redhat.com>
---
 arch/arm64/kernel/vmlinux.lds.S | 31 +++++++------------------------
 1 file changed, 7 insertions(+), 24 deletions(-)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index f8ab9d8..4ff9dcf 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -97,30 +97,13 @@ SECTIONS
 	PERCPU_SECTION(64)
 
 	__init_end = .;
-	. = ALIGN(THREAD_SIZE);
-	__data_loc = .;
-
-	.data : AT(__data_loc) {
-		_data = .;		/* address in memory */
-		_sdata = .;
-
-		/*
-		 * first, the init task union, aligned
-		 * to an 8192 byte boundary.
-		 */
-		INIT_TASK_DATA(THREAD_SIZE)
-		NOSAVE_DATA
-		CACHELINE_ALIGNED_DATA(64)
-		READ_MOSTLY_DATA(64)
-
-		/*
-		 * and the usual data section
-		 */
-		DATA_DATA
-		CONSTRUCTORS
-
-		_edata = .;
-	}
+
+	. = ALIGN(PAGE_SIZE);
+	_data = .;
+	__data_loc = _data - LOAD_OFFSET;
+	_sdata = .;
+	RW_DATA_SECTION(64, PAGE_SIZE, THREAD_SIZE)
+	_edata = .;
 	_edata_loc = __data_loc + SIZEOF(.data);
 
 	BSS_SECTION(0, 0, 0)
-- 
1.8.3.1

Re: [PATCH] arm64: use generic RW_DATA_SECTION macro in linker script

[Will Deacon]

On Mon, Nov 04, 2013 at 04:38:47PM +0000, Mark Salter wrote:
> The .data section in the arm64 linker script currently lacks a
> definition for page-aligned data. This leads to a .page_aligned
> section being placed between the end of data and start of bss.
> This patch corrects that by using the generic RW_DATA_SECTION
> macro which includes support for page-aligned data.
> 
> Signed-off-by: Mark Salter <msalter@redhat.com>

  Acked-by: Will Deacon <will.deacon@arm.com>

Cheers Mark!

Will

Re: [PATCH] arm64: use generic RW_DATA_SECTION macro in linker script

[Catalin Marinas]

On Mon, Nov 04, 2013 at 04:38:47PM +0000, Mark Salter wrote:
> The .data section in the arm64 linker script currently lacks a
> definition for page-aligned data. This leads to a .page_aligned
> section being placed between the end of data and start of bss.
> This patch corrects that by using the generic RW_DATA_SECTION
> macro which includes support for page-aligned data.
> 
> Signed-off-by: Mark Salter <msalter@redhat.com>

Thanks. Applied.

-- 
Catalin