linux-kernel - Re: [PATCH 10/43] kmsan: pgtable: reduce vmalloc space

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Message-ID: <YbnvTso+V6eZYGt+@FVFF77S0Q05N>
Date:   Wed, 15 Dec 2021 13:36:14 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/43] kmsan: pgtable: reduce vmalloc space

On Tue, Dec 14, 2021 at 05:20:17PM +0100, Alexander Potapenko wrote:
> KMSAN is going to use 3/4 of existing vmalloc space to hold the
> metadata, therefore we lower VMALLOC_END to make sure vmalloc() doesn't
> allocate past the first 1/4.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>

It might be worth adding an 'x86: ' prefix to the commit title, since this
specifically affects x86 headers.

Mark.

> ---
> Link: https://linux-review.googlesource.com/id/I9d8b7f0a88a639f1263bc693cbd5c136626f7efd
> ---
>  arch/x86/include/asm/pgtable_64_types.h | 41 ++++++++++++++++++++++++-
>  arch/x86/mm/init_64.c                   |  2 +-
>  2 files changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 91ac106545703..7f15d43754a34 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -139,7 +139,46 @@ extern unsigned int ptrs_per_p4d;
>  # define VMEMMAP_START		__VMEMMAP_BASE_L4
>  #endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
>  
> -#define VMALLOC_END		(VMALLOC_START + (VMALLOC_SIZE_TB << 40) - 1)
> +#define VMEMORY_END		(VMALLOC_START + (VMALLOC_SIZE_TB << 40) - 1)
> +
> +#ifndef CONFIG_KMSAN
> +#define VMALLOC_END		VMEMORY_END
> +#else
> +/*
> + * In KMSAN builds vmalloc area is four times smaller, and the remaining 3/4
> + * are used to keep the metadata for virtual pages. The memory formerly
> + * belonging to vmalloc area is now laid out as follows:
> + *
> + * 1st quarter: VMALLOC_START to VMALLOC_END - new vmalloc area
> + * 2nd quarter: KMSAN_VMALLOC_SHADOW_START to
> + *              VMALLOC_END+KMSAN_VMALLOC_SHADOW_OFFSET - vmalloc area shadow
> + * 3rd quarter: KMSAN_VMALLOC_ORIGIN_START to
> + *              VMALLOC_END+KMSAN_VMALLOC_ORIGIN_OFFSET - vmalloc area origins
> + * 4th quarter: KMSAN_MODULES_SHADOW_START to KMSAN_MODULES_ORIGIN_START
> + *              - shadow for modules,
> + *              KMSAN_MODULES_ORIGIN_START to
> + *              KMSAN_MODULES_ORIGIN_START + MODULES_LEN - origins for modules.
> + */
> +#define VMALLOC_QUARTER_SIZE	((VMALLOC_SIZE_TB << 40) >> 2)
> +#define VMALLOC_END		(VMALLOC_START + VMALLOC_QUARTER_SIZE - 1)
> +
> +/*
> + * vmalloc metadata addresses are calculated by adding shadow/origin offsets
> + * to vmalloc address.
> + */
> +#define KMSAN_VMALLOC_SHADOW_OFFSET	VMALLOC_QUARTER_SIZE
> +#define KMSAN_VMALLOC_ORIGIN_OFFSET	(VMALLOC_QUARTER_SIZE << 1)
> +
> +#define KMSAN_VMALLOC_SHADOW_START	(VMALLOC_START + KMSAN_VMALLOC_SHADOW_OFFSET)
> +#define KMSAN_VMALLOC_ORIGIN_START	(VMALLOC_START + KMSAN_VMALLOC_ORIGIN_OFFSET)
> +
> +/*
> + * The shadow/origin for modules are placed one by one in the last 1/4 of
> + * vmalloc space.
> + */
> +#define KMSAN_MODULES_SHADOW_START	(VMALLOC_END + KMSAN_VMALLOC_ORIGIN_OFFSET + 1)
> +#define KMSAN_MODULES_ORIGIN_START	(KMSAN_MODULES_SHADOW_START + MODULES_LEN)
> +#endif /* CONFIG_KMSAN */
>  
>  #define MODULES_VADDR		(__START_KERNEL_map + KERNEL_IMAGE_SIZE)
>  /* The module sections ends with the start of the fixmap */
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 36098226a9573..8e884e44a8d1e 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1287,7 +1287,7 @@ static void __init preallocate_vmalloc_pages(void)
>  	unsigned long addr;
>  	const char *lvl;
>  
> -	for (addr = VMALLOC_START; addr <= VMALLOC_END; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
> +	for (addr = VMALLOC_START; addr <= VMEMORY_END; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
>  		pgd_t *pgd = pgd_offset_k(addr);
>  		p4d_t *p4d;
>  		pud_t *pud;
> -- 
> 2.34.1.173.g76aa8bc2d0-goog
>