linux-kernel - Re: [RFC PATCH v1 44/57] arm64: Align sections to PAGE_SIZE

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Message-ID: <69533deb-dc77-49c3-a256-49efee308905@t-8ch.de>
Date: Sat, 19 Oct 2024 14:16:42 +0000
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Anshuman Khandual <anshuman.khandual@....com>, Ard Biesheuvel <ardb@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, David Hildenbrand <david@...hat.com>, 
	Greg Marsden <greg.marsden@...cle.com>, Ivan Ivanov <ivan.ivanov@...e.com>, 
	Kalesh Singh <kaleshsingh@...gle.com>, Marc Zyngier <maz@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Matthias Brugger <mbrugger@...e.com>, 
	Miroslav Benes <mbenes@...e.cz>, Oliver Upton <oliver.upton@...ux.dev>, 
	Will Deacon <will@...nel.org>, kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v1 44/57] arm64: Align sections to PAGE_SIZE_MAX

On 2024-10-14 11:58:51+0100, Ryan Roberts wrote:
> Increase alignment of sections in nvhe hyp, vdso and final vmlinux image
> from PAGE_SIZE to PAGE_SIZE_MAX. For compile-time PAGE_SIZE,
> PAGE_SIZE_MAX == PAGE_SIZE so there is no change. For boot-time
> PAGE_SIZE, PAGE_SIZE_MAX is the largest selectable page size.
> 
> For a boot-time page size build, image size is comparable to a 64K page
> size compile-time build. In future, it may be desirable to optimize
> run-time memory consumption by freeing unused padding pages when the
> boot-time selected page size is less than PAGE_SIZE_MAX.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
> 
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
> 
>  arch/arm64/include/asm/memory.h     |  4 +--
>  arch/arm64/kernel/vdso-wrap.S       |  4 +--
>  arch/arm64/kernel/vdso.c            |  7 +++---
>  arch/arm64/kernel/vdso/vdso.lds.S   |  4 +--
>  arch/arm64/kernel/vdso32-wrap.S     |  4 +--
>  arch/arm64/kernel/vdso32/vdso.lds.S |  4 +--
>  arch/arm64/kernel/vmlinux.lds.S     | 38 ++++++++++++++---------------
>  arch/arm64/kvm/hyp/nvhe/hyp.lds.S   |  2 +-
>  8 files changed, 34 insertions(+), 33 deletions(-)

> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index 89b6e78400023..1efe98909a2e0 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -195,7 +195,7 @@ static int __setup_additional_pages(enum vdso_abi abi,
>  
>  	vdso_text_len = vdso_info[abi].vdso_pages << PAGE_SHIFT;
>  	/* Be sure to map the data page */
> -	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE;
> +	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE_MAX;
>  
>  	vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
>  	if (IS_ERR_VALUE(vdso_base)) {
> @@ -203,7 +203,8 @@ static int __setup_additional_pages(enum vdso_abi abi,
>  		goto up_fail;
>  	}
>  
> -	ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE,
> +	ret = _install_special_mapping(mm, vdso_base,
> +				       VVAR_NR_PAGES * PAGE_SIZE_MAX,
>  				       VM_READ|VM_MAYREAD|VM_PFNMAP,
>  				       vdso_info[abi].dm);
>  	if (IS_ERR(ret))
> @@ -212,7 +213,7 @@ static int __setup_additional_pages(enum vdso_abi abi,
>  	if (system_supports_bti_kernel())
>  		gp_flags = VM_ARM64_BTI;
>  
> -	vdso_base += VVAR_NR_PAGES * PAGE_SIZE;
> +	vdso_base += VVAR_NR_PAGES * PAGE_SIZE_MAX;
>  	mm->context.vdso = (void *)vdso_base;
>  	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
>  				       VM_READ|VM_EXEC|gp_flags|

> diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
> index 45354f2ddf706..f7d1537a689e8 100644
> --- a/arch/arm64/kernel/vdso/vdso.lds.S
> +++ b/arch/arm64/kernel/vdso/vdso.lds.S
> @@ -18,9 +18,9 @@ OUTPUT_ARCH(aarch64)
>  
>  SECTIONS
>  {
> -	PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
> +	PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE_MAX);
>  #ifdef CONFIG_TIME_NS
> -	PROVIDE(_timens_data = _vdso_data + PAGE_SIZE);
> +	PROVIDE(_timens_data = _vdso_data + PAGE_SIZE_MAX);

This looks like it also needs a change to vvar_fault() in vdso.c.
The symbols are now always PAGE_SIZE_MAX apart, while vvar_fault() works
in page offsets (vmf->pgoff) that are based on the runtime PAGE_SIZE and
it expects hardcoded offsets.

As test you can use tools/testing/selftests/timens/timens.

(I can't test this right now, so it's only a suspicion)

>  #endif
>  	. = VDSO_LBASE + SIZEOF_HEADERS;

> diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
> index 8d95d7d35057d..c46d18a69d1ce 100644
> --- a/arch/arm64/kernel/vdso32/vdso.lds.S
> +++ b/arch/arm64/kernel/vdso32/vdso.lds.S
> @@ -18,9 +18,9 @@ OUTPUT_ARCH(arm)
>  
>  SECTIONS
>  {
> -	PROVIDE_HIDDEN(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
> +	PROVIDE_HIDDEN(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE_MAX);
>  #ifdef CONFIG_TIME_NS
> -	PROVIDE_HIDDEN(_timens_data = _vdso_data + PAGE_SIZE);
> +	PROVIDE_HIDDEN(_timens_data = _vdso_data + PAGE_SIZE_MAX);
>  #endif
>  	. = VDSO_LBASE + SIZEOF_HEADERS;