linux-kernel - Re: [PATCH v2 RESEND 2/2] x86/mm/KASLR: Do not adapt the size of the direct mapping section for SGI UV system

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Date:   Sat, 30 Sep 2017 19:25:04 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Mike Travis <mike.travis@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, rja@....com, frank.ramsay@....com,
        linux-kernel@...r.kernel.org, x86@...nel.org, mingo@...hat.com,
        tglx@...utronix.de, hpa@...or.com, thgarnie@...gle.com,
        keescook@...omium.org, akpm@...ux-foundation.org,
        yamada.masahiro@...ionext.com, sivanich@....com
Subject: Re: [PATCH v2 RESEND 2/2] x86/mm/KASLR: Do not adapt the size of the
 direct mapping section for SGI UV system

Hi Mike,

On 09/28/17 at 07:10am, Mike Travis wrote:
> 
> 
> On 9/28/2017 2:01 AM, Ingo Molnar wrote:
> > 
> > > If on SGI UV system, the kaslr_regions[0].size_tb, namely the size of
> > > the direct mapping section, is incorrect.
> > > 
> > > Its direct mapping size includes two parts:
> > > #1 RAM size of system
> > > #2 MMIOH region size which only SGI UV system has.
> > > 
> > > However, the #2 can only be got till uv_system_init() is called in
> > > native_smp_prepare_cpus(). That is too late for mm KASLR calculation.
> > > That's why I made this hack.
> > > 
> > > I checked uv_system_init() code, seems not easy to know the size of
> > > MMIOH region before or inside kernel_randomize_memory(). I have CCed UV
> > > devel experts, not sure if they have any idea about this. Otherwise,
> > > this patch could be the only way I can think of.
> > > 
> > > Hi Mike and Russ,
> > > 
> > > Is there any chance we can get the size of MMIOH region before mm KASLR
> > > code, namely before we call kernel_randomize_memory()?
> 
> The sizes of the MMIOL and MMIOH areas are tied into the HUB design and how
> it is communicated to BIOS and the kernel.  This is via some of the config
> MMR's found in the HUB and it would be impossible to provide any access to
> these registers as they change with each new UV architecture.
> 
> The kernel does reserve the memory in the EFI memmap.  I can send you a
> console log of the full startup that includes the MMIOH reservations. Note
> that it is dependent on what I/O devices are actually present as UV does not
> map empty slots unless forced (because we'd quickly run out of resources.)
> Also, the EFI memmap entries do not specify the exact usage of the contained
> areas.

Does that mean we can get the size of MMIOH from efi entries? If yes,
please help provide a console log including those. If can get size from
efi, it will be more acceptable.

Or I can ask Frank to loan his uv system to me, not sure if he is doing
testing with them.

Thanks
Baoquan

> 
> > 
> > I don't mind system specific quirks to hardware enumeration details, as long as
> > they don't pollute generic code with such special hacks.
> > 
> > I.e. in this case it's wrong to allow kaslr_regions[0].size_tb to be wrong. Any
> > other code that relies on it in the future will be wrong as well on UV systems.
> 
> Which may come into play on other arches with the new upcoming memory
> technologies.
> > 
> > The right quirk would be to fix that up where it gets introduced, or something
> > like that.
> 
> Yes, does make sense.
> > 
> > Thanks,
> > 
> > 	Ingo
> >