linux-kernel - Re: [PATCH 1/2] x86/mm: Move LDT remap out of KASLR region on 5-level paging

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Message-ID: <20181024124443.husnnxgligsncm5t@kshutemo-mobl1>
Date:   Wed, 24 Oct 2018 15:44:43 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/mm: Move LDT remap out of KASLR region on
 5-level paging

On Wed, Oct 24, 2018 at 04:54:47AM -0700, Matthew Wilcox wrote:
> On Tue, Oct 23, 2018 at 07:31:56PM +0300, Kirill A. Shutemov wrote:
> > -ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
> > +ffff888000000000 - ffff887fffffffff (=39 bits) LDT remap for PTI
> 
> I'm a little bit cross-eyed at this point, but I think the above '888'
> should be '880'.
> 
> > @@ -14,7 +15,6 @@ ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB)
> >  ... unused hole ...
> >  				    vaddr_end for KASLR
> >  fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping
> > -fffffe8000000000 - fffffeffffffffff (=39 bits) LDT remap for PTI
> 
> ... and the line above this one should be adjusted to finish at
> fffffeffffffffff (also it's now 40 bits).  Or should there be something
> else here?
> 
> >  ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
> >  ... unused hole ...
> >  ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
> > @@ -30,8 +30,8 @@ Virtual memory map with 5 level page tables:
> >  0000000000000000 - 00ffffffffffffff (=56 bits) user space, different per mm
> >  hole caused by [56:63] sign extension
> >  ff00000000000000 - ff0fffffffffffff (=52 bits) guard hole, reserved for hypervisor
> > -ff10000000000000 - ff8fffffffffffff (=55 bits) direct mapping of all phys. memory
> > -ff90000000000000 - ff9fffffffffffff (=52 bits) LDT remap for PTI
> > +ff10000000000000 - ff10ffffffffffff (=48 bits) LDT remap for PTI
> > +ff11000000000000 - ff90ffffffffffff (=55 bits) direct mapping of all phys. memory
> 
> What's at ff910..0 to ff9f..f ?
> 
> Is there any way we can generate this part of this file to prevent human
> error from creeping in over time?  ;-)

In current Linus' tree this part of the documentation was re-written. I've
rebased to it and rewrote the documenation for the change.

I believe I've fixed all mistakes you've noticied. Please check out v2. I
will post it soon.

-- 
 Kirill A. Shutemov