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From:   Marco Elver <elver@google.com>
Date:   Mon, 11 Jul 2022 18:12:59 +0200
Message-ID: <CANpmjNN8xD2WK_Au86ww1eqGaUbWr+B=m0GuzrDrbhKA=hJYwQ@mail.gmail.com>
Subject: Re: [PATCH v4 09/45] x86: kmsan: pgtable: reduce vmalloc space
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.com> 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@google.com>
> ---
> v2:
>  -- added x86: to the title
>
> 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 70e360a2e5fb7..ad6ded5b1dedf 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)

Comment what VMEMORY_END is? (Seems obvious, but less guessing is better here.)

> +#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 39c5246964a91..5806331172361 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;
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>