LinuxLists.cc - [PATCH] arm64: move kimage

2020-03-12 09:51:58

Subject: [PATCH] arm64: move kimage_vaddr to .rodata

From: Remi Denis-Courmont <[email protected]>

This datum is not referenced from .idmap.text: it does not need to be
mapped in idmap. Lets move it to .rodata as it is never written to after
early boot of the primary CPU.
(Maybe .data.ro_after_init would be cleaner though?)

Signed-off-by: Rémi Denis-Courmont <[email protected]>
---
arch/arm64/kernel/head.S | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 6e08ee2b4d55..8e5c0e0040e4 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -457,17 +457,19 @@ SYM_FUNC_START_LOCAL(__primary_switched)
b start_kernel
SYM_FUNC_END(__primary_switched)

+ .pushsection ".rodata", "a"
+SYM_DATA_START(kimage_vaddr)
+ .quad _text - TEXT_OFFSET
+SYM_DATA_END(kimage_vaddr)
+EXPORT_SYMBOL(kimage_vaddr)
+ .popsection
+
/*
* end early head section, begin head code that is also used for
* hotplug and needs to have the same protections as the text region
*/
.section ".idmap.text","awx"

-SYM_DATA_START(kimage_vaddr)
- .quad _text - TEXT_OFFSET
-SYM_DATA_END(kimage_vaddr)
-EXPORT_SYMBOL(kimage_vaddr)
-
/*
* If we're fortunate enough to boot at EL2, ensure that the world is
* sane before dropping to EL1.
--
2.25.1

2020-03-12 16:41:52

by Mark Rutland

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Subject: Re: [PATCH] arm64: move kimage_vaddr to .rodata

On Thu, Mar 12, 2020 at 11:40:02AM +0200, Rémi Denis-Courmont wrote:
> From: Remi Denis-Courmont <[email protected]>
>
> This datum is not referenced from .idmap.text: it does not need to be
> mapped in idmap. Lets move it to .rodata as it is never written to after
> early boot of the primary CPU.
> (Maybe .data.ro_after_init would be cleaner though?)

Can we move this into arch/arm64/mm/mmu.c, where we already have
kimage_voffset:

| u64 kimage_voffset __ro_after_init;
| EXPORT_SYMBOL(kimage_voffset);

... or is it not possible to initialize kimage_vaddr correctly in C?

Thanks,
Mark.

>
> Signed-off-by: Rémi Denis-Courmont <[email protected]>
> ---
> arch/arm64/kernel/head.S | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 6e08ee2b4d55..8e5c0e0040e4 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -457,17 +457,19 @@ SYM_FUNC_START_LOCAL(__primary_switched)
> b start_kernel
> SYM_FUNC_END(__primary_switched)
>
> + .pushsection ".rodata", "a"
> +SYM_DATA_START(kimage_vaddr)
> + .quad _text - TEXT_OFFSET
> +SYM_DATA_END(kimage_vaddr)
> +EXPORT_SYMBOL(kimage_vaddr)
> + .popsection
> +
> /*
> * end early head section, begin head code that is also used for
> * hotplug and needs to have the same protections as the text region
> */
> .section ".idmap.text","awx"
>
> -SYM_DATA_START(kimage_vaddr)
> - .quad _text - TEXT_OFFSET
> -SYM_DATA_END(kimage_vaddr)
> -EXPORT_SYMBOL(kimage_vaddr)
> -
> /*
> * If we're fortunate enough to boot at EL2, ensure that the world is
> * sane before dropping to EL1.
> --
> 2.25.1
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

2020-03-12 16:44:03

by Rémi Denis-Courmont

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Subject: Re: [PATCH] arm64: move kimage_vaddr to .rodata

Le 2020-03-12 18:40, Mark Rutland a écrit :
> On Thu, Mar 12, 2020 at 11:40:02AM +0200, Rémi Denis-Courmont wrote:
>> From: Remi Denis-Courmont <[email protected]>
>>
>> This datum is not referenced from .idmap.text: it does not need to be
>> mapped in idmap. Lets move it to .rodata as it is never written to
>> after
>> early boot of the primary CPU.
>> (Maybe .data.ro_after_init would be cleaner though?)
>
> Can we move this into arch/arm64/mm/mmu.c, where we already have
> kimage_voffset:
>
> | u64 kimage_voffset __ro_after_init;
> | EXPORT_SYMBOL(kimage_voffset);
>
> ... or is it not possible to initialize kimage_vaddr correctly in C?

Good question... I'll check tomorrow.

--
Rémi Denis-Courmont

2020-03-16 10:33:58

by Rémi Denis-Courmont

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Subject: Re: [PATCH] arm64: move kimage_vaddr to .rodata

Le torstaina 12. maaliskuuta 2020, 18.40.36 EET Mark Rutland a écrit :
> On Thu, Mar 12, 2020 at 11:40:02AM +0200, Rémi Denis-Courmont wrote:
> > From: Remi Denis-Courmont <[email protected]>
> >
> > This datum is not referenced from .idmap.text: it does not need to be
> > mapped in idmap. Lets move it to .rodata as it is never written to after
> > early boot of the primary CPU.
> > (Maybe .data.ro_after_init would be cleaner though?)
>
> Can we move this into arch/arm64/mm/mmu.c, where we already have
>
> kimage_voffset:
> | u64 kimage_voffset __ro_after_init;
> | EXPORT_SYMBOL(kimage_voffset);
>
> ... or is it not possible to initialize kimage_vaddr correctly in C?

Currently TEXT_OFFSET is defined by the Makefile only for assembler sources and
the linker script. So that would need to be exposed to CPPFLAGS as well.

--
Реми Дёни-Курмон
http://www.remlab.net/

2020-03-17 22:29:40

by Will Deacon

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Subject: Re: [PATCH] arm64: move kimage_vaddr to .rodata

On Thu, Mar 12, 2020 at 11:40:02AM +0200, R?mi Denis-Courmont wrote:
> From: Remi Denis-Courmont <[email protected]>
>
> This datum is not referenced from .idmap.text: it does not need to be
> mapped in idmap. Lets move it to .rodata as it is never written to after
> early boot of the primary CPU.
> (Maybe .data.ro_after_init would be cleaner though?)
>
> Signed-off-by: R?mi Denis-Courmont <[email protected]>
> ---
> arch/arm64/kernel/head.S | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 6e08ee2b4d55..8e5c0e0040e4 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -457,17 +457,19 @@ SYM_FUNC_START_LOCAL(__primary_switched)
> b start_kernel
> SYM_FUNC_END(__primary_switched)
>
> + .pushsection ".rodata", "a"
> +SYM_DATA_START(kimage_vaddr)
> + .quad _text - TEXT_OFFSET
> +SYM_DATA_END(kimage_vaddr)
> +EXPORT_SYMBOL(kimage_vaddr)
> + .popsection
> +
> /*
> * end early head section, begin head code that is also used for
> * hotplug and needs to have the same protections as the text region
> */
> .section ".idmap.text","awx"
>
> -SYM_DATA_START(kimage_vaddr)
> - .quad _text - TEXT_OFFSET
> -SYM_DATA_END(kimage_vaddr)
> -EXPORT_SYMBOL(kimage_vaddr)

Acked-by: Will Deacon <[email protected]>

Will

2020-03-20 18:25:56

by Catalin Marinas

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