diff mbox

[v4,4/7] arm64: Add a description on 48-bit address space with 4KB pages

Message ID 000401cf6367$cc461500$64d23f00$@samsung.com (mailing list archive)
State New, archived
Headers show

Commit Message

??? April 29, 2014, 4:59 a.m. UTC 
This patch adds memory layout and translation lookup information
about 48-bit address space with 4K pages. The description is based
on 4 levels of translation tables.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steve Capper <steve.capper@linaro.org>
Signed-off-by: Jungseok Lee <jays.lee@samsung.com>
Reviewed-by: Sungjinn Chung <sungjinn.chung@samsung.com>
---
 Documentation/arm64/memory.txt |   59 ++++++++++++++++++++++++++++++++++------
 1 file changed, 51 insertions(+), 8 deletions(-)

Comments

Catalin Marinas April 29, 2014, 2:47 p.m. UTC | #1 
On Tue, Apr 29, 2014 at 05:59:27AM +0100, Jungseok Lee wrote:
> --- a/Documentation/arm64/memory.txt
> +++ b/Documentation/arm64/memory.txt
> @@ -8,10 +8,11 @@ This document describes the virtual memory layout used by the AArch64
>  Linux kernel. The architecture allows up to 4 levels of translation
>  tables with a 4KB page size and up to 3 levels with a 64KB page size.
>  
> -AArch64 Linux uses 3 levels of translation tables with the 4KB page
> -configuration, allowing 39-bit (512GB) virtual addresses for both user
> -and kernel. With 64KB pages, only 2 levels of translation tables are
> -used but the memory layout is the same.
> +AArch64 Linux uses 3 levels and 4 levels of translation tables with
> +the 4KB page configuration, allowing 39-bit (512GB) and 48-bit (256TB)
> +virtual addresses, respectively, for both user and kernel. With 64KB
> +pages, only 2 levels of translation tables are used but the memory layout
> +is the same.

Any reason why we couldn't use 48-bit address space with 64K pages
(implying 3 levels)?

> -AArch64 Linux memory layout with 64KB pages:
> +AArch64 Linux memory layout with 4KB pages + 4 levels:
> +
> +Start			End			Size		Use
> +-----------------------------------------------------------------------
> +0000000000000000	0000ffffffffffff	 256TB		user
> +
> +ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc

BTW, maybe as a separate patch we should change the "end" to be
exclusive. It becomes harder to modify (I've been through this a few
times already ;)) and even follow the changes.
??? April 30, 2014, 6:41 a.m. UTC | #2 
On Tuesday, April 29, 2014 11:48 PM, Catalin Marinas wrote:
> On Tue, Apr 29, 2014 at 05:59:27AM +0100, Jungseok Lee wrote:
> > --- a/Documentation/arm64/memory.txt
> > +++ b/Documentation/arm64/memory.txt
> > @@ -8,10 +8,11 @@ This document describes the virtual memory layout
> > used by the AArch64  Linux kernel. The architecture allows up to 4
> > levels of translation  tables with a 4KB page size and up to 3 levels with a 64KB page size.
> >
> > -AArch64 Linux uses 3 levels of translation tables with the 4KB page
> > -configuration, allowing 39-bit (512GB) virtual addresses for both
> > user -and kernel. With 64KB pages, only 2 levels of translation tables
> > are -used but the memory layout is the same.
> > +AArch64 Linux uses 3 levels and 4 levels of translation tables with
> > +the 4KB page configuration, allowing 39-bit (512GB) and 48-bit
> > +(256TB) virtual addresses, respectively, for both user and kernel.
> > +With 64KB pages, only 2 levels of translation tables are used but the
> > +memory layout is the same.
> 
> Any reason why we couldn't use 48-bit address space with 64K pages (implying 3 levels)?

No technical reason.
Since 64K+3levels is not implemented in this set, I didn't add it.

Should 64K+3levels be prepared in this patchset?

> > -AArch64 Linux memory layout with 64KB pages:
> > +AArch64 Linux memory layout with 4KB pages + 4 levels:
> > +
> > +Start			End			Size		Use
> > +-----------------------------------------------------------------------
> > +0000000000000000	0000ffffffffffff	 256TB		user
> > +
> > +ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc
> 
> BTW, maybe as a separate patch we should change the "end" to be exclusive. It becomes harder to modify
> (I've been through this a few times already ;)) and even follow the changes.

Does "exclusive" mean that 0000ffffffffffff is changed to 0001000000000000?
Or Does it mean that "End" column is dropped?

If you are okay, I will make it as a separate patch.

Best Regards
Jungseok Lee

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Catalin Marinas April 30, 2014, 1:12 p.m. UTC | #3 
On Wed, Apr 30, 2014 at 07:41:40AM +0100, Jungseok Lee wrote:
> On Tuesday, April 29, 2014 11:48 PM, Catalin Marinas wrote:
> > On Tue, Apr 29, 2014 at 05:59:27AM +0100, Jungseok Lee wrote:
> > > --- a/Documentation/arm64/memory.txt
> > > +++ b/Documentation/arm64/memory.txt
> > > @@ -8,10 +8,11 @@ This document describes the virtual memory layout
> > > used by the AArch64  Linux kernel. The architecture allows up to 4
> > > levels of translation  tables with a 4KB page size and up to 3 levels with a 64KB page size.
> > >
> > > -AArch64 Linux uses 3 levels of translation tables with the 4KB page
> > > -configuration, allowing 39-bit (512GB) virtual addresses for both
> > > user -and kernel. With 64KB pages, only 2 levels of translation tables
> > > are -used but the memory layout is the same.
> > > +AArch64 Linux uses 3 levels and 4 levels of translation tables with
> > > +the 4KB page configuration, allowing 39-bit (512GB) and 48-bit
> > > +(256TB) virtual addresses, respectively, for both user and kernel.
> > > +With 64KB pages, only 2 levels of translation tables are used but the
> > > +memory layout is the same.
> > 
> > Any reason why we couldn't use 48-bit address space with 64K pages (implying 3 levels)?
> 
> No technical reason.
> Since 64K+3levels is not implemented in this set, I didn't add it.
> 
> Should 64K+3levels be prepared in this patchset?
> 
> > > -AArch64 Linux memory layout with 64KB pages:
> > > +AArch64 Linux memory layout with 4KB pages + 4 levels:
> > > +
> > > +Start			End			Size		Use
> > > +-----------------------------------------------------------------------
> > > +0000000000000000	0000ffffffffffff	 256TB		user
> > > +
> > > +ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc
> > 
> > BTW, maybe as a separate patch we should change the "end" to be exclusive. It becomes harder to modify
> > (I've been through this a few times already ;)) and even follow the changes.
> 
> Does "exclusive" mean that 0000ffffffffffff is changed to 0001000000000000?
> Or Does it mean that "End" column is dropped?

Not dropped but changed to 0001.... (the kernel already prints the
memory layout in a similar way).
??? May 1, 2014, 12:53 a.m. UTC | #4 
On Wednesday, April 30, 2014 10:12 PM, Catalin Marinas wrote:
> On Wed, Apr 30, 2014 at 07:41:40AM +0100, Jungseok Lee wrote:
> > On Tuesday, April 29, 2014 11:48 PM, Catalin Marinas wrote:
> > > On Tue, Apr 29, 2014 at 05:59:27AM +0100, Jungseok Lee wrote:
> > > > --- a/Documentation/arm64/memory.txt
> > > > +++ b/Documentation/arm64/memory.txt
> > > > @@ -8,10 +8,11 @@ This document describes the virtual memory
> > > > layout used by the AArch64  Linux kernel. The architecture allows
> > > > up to 4 levels of translation  tables with a 4KB page size and up to 3 levels with a 64KB page
> size.
> > > >
> > > > -AArch64 Linux uses 3 levels of translation tables with the 4KB
> > > > page -configuration, allowing 39-bit (512GB) virtual addresses for
> > > > both user -and kernel. With 64KB pages, only 2 levels of
> > > > translation tables are -used but the memory layout is the same.
> > > > +AArch64 Linux uses 3 levels and 4 levels of translation tables
> > > > +with the 4KB page configuration, allowing 39-bit (512GB) and
> > > > +48-bit
> > > > +(256TB) virtual addresses, respectively, for both user and kernel.
> > > > +With 64KB pages, only 2 levels of translation tables are used but
> > > > +the memory layout is the same.
> > >
> > > Any reason why we couldn't use 48-bit address space with 64K pages (implying 3 levels)?
> >
> > No technical reason.
> > Since 64K+3levels is not implemented in this set, I didn't add it.
> >
> > Should 64K+3levels be prepared in this patchset?
> >
> > > > -AArch64 Linux memory layout with 64KB pages:
> > > > +AArch64 Linux memory layout with 4KB pages + 4 levels:
> > > > +
> > > > +Start			End			Size		Use
> > > > +-----------------------------------------------------------------------
> > > > +0000000000000000	0000ffffffffffff	 256TB		user
> > > > +
> > > > +ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc
> > >
> > > BTW, maybe as a separate patch we should change the "end" to be
> > > exclusive. It becomes harder to modify (I've been through this a few times already ;)) and even
> follow the changes.
> >
> > Does "exclusive" mean that 0000ffffffffffff is changed to 0001000000000000?
> > Or Does it mean that "End" column is dropped?
> 
> Not dropped but changed to 0001.... (the kernel already prints the memory layout in a similar way).

I see. I will make it as a separate patch.

Best Regards
Jungseok Lee

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diff mbox

Patch

diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt
index d50fa61..8142709 100644
--- a/Documentation/arm64/memory.txt
+++ b/Documentation/arm64/memory.txt
@@ -8,10 +8,11 @@  This document describes the virtual memory layout used by the AArch64
 Linux kernel. The architecture allows up to 4 levels of translation
 tables with a 4KB page size and up to 3 levels with a 64KB page size.
 
-AArch64 Linux uses 3 levels of translation tables with the 4KB page
-configuration, allowing 39-bit (512GB) virtual addresses for both user
-and kernel. With 64KB pages, only 2 levels of translation tables are
-used but the memory layout is the same.
+AArch64 Linux uses 3 levels and 4 levels of translation tables with
+the 4KB page configuration, allowing 39-bit (512GB) and 48-bit (256TB)
+virtual addresses, respectively, for both user and kernel. With 64KB
+pages, only 2 levels of translation tables are used but the memory layout
+is the same.
 
 User addresses have bits 63:39 set to 0 while the kernel addresses have
 the same bits set to 1. TTBRx selection is given by bit 63 of the
@@ -21,7 +22,7 @@  The swapper_pgd_dir address is written to TTBR1 and never written to
 TTBR0.
 
 
-AArch64 Linux memory layout with 4KB pages:
+AArch64 Linux memory layout with 4KB pages + 3 levels:
 
 Start			End			Size		Use
 -----------------------------------------------------------------------
@@ -48,7 +49,34 @@  ffffffbffc000000	ffffffbfffffffff	  64MB		modules
 ffffffc000000000	ffffffffffffffff	 256GB		kernel logical memory map
 
 
-AArch64 Linux memory layout with 64KB pages:
+AArch64 Linux memory layout with 4KB pages + 4 levels:
+
+Start			End			Size		Use
+-----------------------------------------------------------------------
+0000000000000000	0000ffffffffffff	 256TB		user
+
+ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc
+
+ffff7bffffff0000	ffff7bffffffffff	  64KB		[guard page]
+
+ffff7c0000000000	ffff7dffffffffff	   2TB		vmemmap
+
+ffff7e0000000000	ffff7ffffbbfffff	  ~2TB		[guard, future vmmemap]
+
+ffff7ffffa000000	ffff7ffffaffffff	  16MB		PCI I/O space
+
+ffff7ffffb000000	ffff7ffffbbfffff	  12MB		[guard]
+
+ffff7ffffbc00000	ffff7ffffbdfffff	   2MB		earlyprintk device
+
+ffff7ffffbe00000	ffff7ffffbffffff	   2MB		[guard]
+
+ffff7ffffc000000	ffff7fffffffffff	  64MB		modules
+
+ffff800000000000	ffffffffffffffff	 128TB		kernel logical memory map
+
+
+AArch64 Linux memory layout with 64KB pages + 2 levels:
 
 Start			End			Size		Use
 -----------------------------------------------------------------------
@@ -75,7 +103,7 @@  fffffdfffc000000	fffffdffffffffff	  64MB		modules
 fffffe0000000000	ffffffffffffffff	   2TB		kernel logical memory map
 
 
-Translation table lookup with 4KB pages:
+Translation table lookup with 4KB pages + 3 levels:
 
 +--------+--------+--------+--------+--------+--------+--------+--------+
 |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
@@ -90,7 +118,22 @@  Translation table lookup with 4KB pages:
  +-------------------------------------------------> [63] TTBR0/1
 
 
-Translation table lookup with 64KB pages:
+Translation table lookup with 4KB pages + 4 levels:
+
++--------+--------+--------+--------+--------+--------+--------+--------+
+|63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
++--------+--------+--------+--------+--------+--------+--------+--------+
+ |                 |         |         |         |         |
+ |                 |         |         |         |         v
+ |                 |         |         |         |   [11:0]  in-page offset
+ |                 |         |         |         +-> [20:12] L3 index
+ |                 |         |         +-----------> [29:21] L2 index
+ |                 |         +---------------------> [38:30] L1 index
+ |                 +-------------------------------> [47:39] L0 index
+ +-------------------------------------------------> [63] TTBR0/1
+
+
+Translation table lookup with 64KB pages + 2 levels:
 
 +--------+--------+--------+--------+--------+--------+--------+--------+
 |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|