arm64: simplify and optimize kernel mapping

This series makes a couple of minor changes that should result in the kernel being mapped in a more efficient manner.

First of all, it merges the .head.text with the .text section (patch #2) after moving everything except the kernel and EFI header into the __init section (patch #1)

Then, it standardizes the segment alignment to 64 KB for all page sizes. (patch #3). In the example below (4 KB granule, with Jeremy's PTE_CONT patch applied), we lose 80 KB in total to padding, but the resulting mappings do look somewhat better.

Before:

0xffff000008082000-0xffff000008090000    56K  ro x  SHD AF         UXN MEM
0xffff000008090000-0xffff000008200000  1472K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008660000   384K  ro x  SHD AF CON     UXN MEM
0xffff000008660000-0xffff00000866c000    48K  ro x  SHD AF         UXN MEM
0xffff00000866c000-0xffff000008670000    16K  ro NX SHD AF         UXN MEM
0xffff000008670000-0xffff000008900000  2624K  ro NX SHD AF CON     UXN MEM
0xffff000008900000-0xffff000008909000    36K  ro NX SHD AF         UXN MEM
0xffff000008c39000-0xffff000008c40000    28K  RW NX SHD AF         UXN MEM
0xffff000008c40000-0xffff000008d50000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d50000-0xffff000008d57000    28K  RW NX SHD AF         UXN MEM

After:

0xffff000008080000-0xffff000008200000  1536K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008670000   448K  ro x  SHD AF CON     UXN MEM
0xffff000008670000-0xffff000008910000  2688K  ro NX SHD AF CON     UXN MEM
0xffff000008c50000-0xffff000008d60000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d60000-0xffff000008d6b000    44K  RW NX SHD AF         UXN MEM

I am aware that this clashes with Jeremy's patch to allow CONT_SIZE alignment when CONFIG_DEBUG_ALIGN_RODATA=y, but the net effect of patch #3 is the same (only the Kconfig change is not included here)

Ard Biesheuvel (3):
arm64: move early boot code to the .init segment
arm64: cover the .head.text section in the .text segment mapping
arm64: simplify kernel segment mapping granularity

 arch/arm64/kernel/efi-entry.S   |  2 +-
 arch/arm64/kernel/head.S        | 32 +++++++++-----------
 arch/arm64/kernel/image.h       |  4 +++
 arch/arm64/kernel/vmlinux.lds.S | 26 +++++++++-------
 arch/arm64/mm/mmu.c             | 10 +++---
 5 files changed, 40 insertions(+), 34 deletions(-)

Signature · 1 line

2.5.0

Hi,

I like this series, though I have a few minor comments below.

Quoted 6 lines · Ard Biesheuvel

This series makes a couple of minor changes that should result in the kernel being mapped in a more efficient manner.

First of all, it merges the .head.text with the .text section (patch #2) after moving everything except the kernel and EFI header into the __init section (patch #1)

Face-to-face, you suggested it might be possible to move .init before .text, so we could place the EFI header in there too (and keep .text aligned while making it smaller). Is there some reason we missed that means we cannot do this?

Quoted 4 lines

Then, it standardizes the segment alignment to 64 KB for all page sizes. (patch #3). In the example below (4 KB granule, with Jeremy's PTE_CONT patch applied), we lose 80 KB in total to padding, but the resulting mappings do look somewhat better.

I suspect some people might want a minimal alignment option for tinification purposes, but this sounds fine to me as a default. I also think we can wait until someone asks.

As a general think, currently we use "chunk" instead of "segment" in the mm code. We only used "chunk" so as to not overload "section". For consistency it would be nice to either keep with "chunk" or convert existing uses to "segment". I much prefer the latter!

Quoted 23 lines

Before:

0xffff000008082000-0xffff000008090000    56K  ro x  SHD AF         UXN MEM
0xffff000008090000-0xffff000008200000  1472K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008660000   384K  ro x  SHD AF CON     UXN MEM
0xffff000008660000-0xffff00000866c000    48K  ro x  SHD AF         UXN MEM
0xffff00000866c000-0xffff000008670000    16K  ro NX SHD AF         UXN MEM
0xffff000008670000-0xffff000008900000  2624K  ro NX SHD AF CON     UXN MEM
0xffff000008900000-0xffff000008909000    36K  ro NX SHD AF         UXN MEM
0xffff000008c39000-0xffff000008c40000    28K  RW NX SHD AF         UXN MEM
0xffff000008c40000-0xffff000008d50000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d50000-0xffff000008d57000    28K  RW NX SHD AF         UXN MEM

After:

0xffff000008080000-0xffff000008200000  1536K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008670000   448K  ro x  SHD AF CON     UXN MEM
0xffff000008670000-0xffff000008910000  2688K  ro NX SHD AF CON     UXN MEM
0xffff000008c50000-0xffff000008d60000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d60000-0xffff000008d6b000    44K  RW NX SHD AF         UXN MEM

Quoted 3 lines

I am aware that this clashes with Jeremy's patch to allow CONT_SIZE alignment when CONFIG_DEBUG_ALIGN_RODATA=y, but the net effect of patch #3 is the same (only the Kconfig change is not included here)

Jeremy, do you have any thoughts on this series?

Hi,

I like this series, though I have a few minor comments below.

Quoted 3 lines · Ard Biesheuvel

This series makes a couple of minor changes that should result in the kernel being mapped in a more efficient manner.

Quoted 3 lines

First of all, it merges the .head.text with the .text section (patch #2) after moving everything except the kernel and EFI header into the __init section (patch #1)

Face-to-face, you suggested it might be possible to move .init before .text, so we could place the EFI header in there too (and keep .text aligned while making it smaller). Is there some reason we missed that means we cannot do this?

Quoted 4 lines

Then, it standardizes the segment alignment to 64 KB for all page sizes. (patch #3). In the example below (4 KB granule, with Jeremy's PTE_CONT patch applied), we lose 80 KB in total to padding, but the resulting mappings do look somewhat better.

I suspect some people might want a minimal alignment option for tinification purposes, but this sounds fine to me as a default. I also think we can wait until someone asks.

As a general think, currently we use "chunk" instead of "segment" in the mm code. We only used "chunk" so as to not overload "section". For consistency it would be nice to either keep with "chunk" or convert existing uses to "segment". I much prefer the latter!

Quoted 23 lines

Before:

0xffff000008082000-0xffff000008090000    56K  ro x  SHD AF         UXN MEM
0xffff000008090000-0xffff000008200000  1472K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008660000   384K  ro x  SHD AF CON     UXN MEM
0xffff000008660000-0xffff00000866c000    48K  ro x  SHD AF         UXN MEM
0xffff00000866c000-0xffff000008670000    16K  ro NX SHD AF         UXN MEM
0xffff000008670000-0xffff000008900000  2624K  ro NX SHD AF CON     UXN MEM
0xffff000008900000-0xffff000008909000    36K  ro NX SHD AF         UXN MEM
0xffff000008c39000-0xffff000008c40000    28K  RW NX SHD AF         UXN MEM
0xffff000008c40000-0xffff000008d50000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d50000-0xffff000008d57000    28K  RW NX SHD AF         UXN MEM

After:

0xffff000008080000-0xffff000008200000  1536K  ro x  SHD AF CON     UXN MEM
0xffff000008200000-0xffff000008600000     4M  ro x  SHD AF     BLK UXN MEM
0xffff000008600000-0xffff000008670000   448K  ro x  SHD AF CON     UXN MEM
0xffff000008670000-0xffff000008910000  2688K  ro NX SHD AF CON     UXN MEM
0xffff000008c50000-0xffff000008d60000  1088K  RW NX SHD AF CON     UXN MEM
0xffff000008d60000-0xffff000008d6b000    44K  RW NX SHD AF         UXN MEM

Quoted 3 lines

I am aware that this clashes with Jeremy's patch to allow CONT_SIZE alignment when CONFIG_DEBUG_ALIGN_RODATA=y, but the net effect of patch #3 is the same (only the Kconfig change is not included here)

Jeremy, do you have any thoughts on this series?

Thanks,
Mark.

Quoted 15 lines

Ard Biesheuvel (3):
arm64: move early boot code to the .init segment
arm64: cover the .head.text section in the .text segment mapping
arm64: simplify kernel segment mapping granularity

 arch/arm64/kernel/efi-entry.S   |  2 +-
 arch/arm64/kernel/head.S        | 32 +++++++++-----------
 arch/arm64/kernel/image.h       |  4 +++
 arch/arm64/kernel/vmlinux.lds.S | 26 +++++++++-------
 arch/arm64/mm/mmu.c             | 10 +++---
 5 files changed, 40 insertions(+), 34 deletions(-)

--
2.5.0