linux-kernel - Re: [PATCH v3 2/2] efi: efi_mem_reserve(): don't reserve through memblock after mm

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Message-ID: <CAKv+Gu8RHsMKmEHBqNv=q4SB-spCtuydbCshs2ut1+Kk8vraOQ@mail.gmail.com>
Date:   Fri, 6 Jan 2017 08:35:52 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Nicolai Stange <nicstange@...il.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Young <dyoung@...hat.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] efi: efi_mem_reserve(): don't reserve through
 memblock after mm_init()

On 5 January 2017 at 12:51, Nicolai Stange <nicstange@...il.com> wrote:
> Before invoking the arch specific handler, efi_mem_reserve() reserves
> the given memory region through memblock.
>
> efi_mem_reserve() can get called after mm_init() though -- through
> efi_bgrt_init(), for example. After mm_init(), memblock is dead and should
> not be used anymore.
>
> Let efi_mem_reserve() check whether memblock is dead and not do the
> reservation if so. Emit a warning from the generic efi_arch mem_reserve()
> in this case: if the architecture doesn't provide any other means of
> registering the region as reserved, the operation would be a nop.
>
> Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> ---
> Applicable to next-20170105.
> No changes to v2.
> Boot-tested on x86_64.
>
>  drivers/firmware/efi/efi.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 92914801e388..158a8df2f4af 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -403,7 +403,10 @@ u64 __init efi_mem_desc_end(efi_memory_desc_t *md)
>         return end;
>  }
>
> -void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size) {}
> +void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size)
> +{
> +       WARN(slab_is_available(), "efi_mem_reserve() has no effect");
> +}
>
>  /**
>   * efi_mem_reserve - Reserve an EFI memory region
> @@ -419,7 +422,7 @@ void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size) {}
>   */
>  void __init efi_mem_reserve(phys_addr_t addr, u64 size)
>  {
> -       if (!memblock_is_region_reserved(addr, size))
> +       if (!slab_is_available() && !memblock_is_region_reserved(addr, size))
>                 memblock_reserve(addr, size);
>

I share Dave's concern: on x86, this will silently ignore the
reservation if slab_is_available() returns true, so we should at least
warn here. I don't think this patch solves any known issues, so I'd
rather defer this for now, and pick up the discussion when Matt is
back,