linux-kernel - Re: [PATCH v2 2/2] efi: efi_mem_reserve(): don't reserve through memblock after mm

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Date:   Tue, 10 Jan 2017 08:37:35 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Nicolai Stange <nicstange@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH v2 2/2] efi: efi_mem_reserve(): don't reserve through
 memblock after mm_init()

On 01/09/17 at 11:44am, Matt Fleming wrote:
> On Thu, 05 Jan, at 05:12:42PM, Dave Young wrote:
> > On 12/22/16 at 11:23am, Nicolai Stange 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.
> > 
> > It did not fail during previous test so we did not catch this bug, if memblock
> > can not be used after mm_init(), IMHO it should fail instead of silently succeed.
>  
> This must literally be the fifth time or so that I've been caught out
> by this over the years because there's no hard error if you call the
> memblock code after slab and co. are up.
> 
> MM folks, is there some way to catch these errors without requiring
> the sprinkling of slab_is_available() everywhere?
> 
> > Matt, can we move the efi_mem_reserve to earlier code for example in
> > efi_memblock_x86_reserve_range just after reserving the memmap?
>  
> No, it *needs* to be callable from efi_bgrt_init(), because you only
> want to reserve those regions if you have the BGRT driver available.

It is true that it depends on acpi init, I was wondering if bgrt parsing can
be moved to early acpi code. But anyway I'm not sure it is doable and
worth.

Thanks
Dave