Re: [PATCH 4.4 00/37] 4.4.110-stable review

[Pavel Tatashin]

On 01/11/2018 03:10 PM, Greg Kroah-Hartman wrote:
> On Thu, Jan 11, 2018 at 01:36:50PM -0500, Pavel Tatashin wrote:
> > I have root caused the memory corruption panics/hangs that I've been
> > experiencing during boot with the latest 4.4.110 kernel. The problem
> > as was suspected by Andy Lutomirski is with interaction between PTI
> > and EFI. It may affect any system that has EFI bios.  I have not
> > verified if it can affect any other kernel beside 4.4.110
> >
> > Attached is the fix for this issue with explanations that Steve
> > Sistare and I developed.
>
> Nice, but why does this not show up in 4.9 and 4.14 and Linus's tree as
> well on this hardware?  Nor on the SLES12 SP3 kernel?
>
> What is different there that 4.4 requires?  That worries me more than
> your fix (which looks good to me, fwiw.)

Hi Greg,

I have not studied other versions of kernels, efi was changed 
substantially since 4.4. But, even on 4.4.110 there are several things 
have to happen for this bug to show-up:

1. During boot memmblock must allocate address that is not 2PAGE_SIZE 
aligned.
2. nmi must arrive exactly when EFI replaced page table.

While I was debugging this problem, I tried to enable, kasan, vm_debug, 
add more printfs etc, but every little change would cause this problem 
to disappear, or appear less frequently.

Thank you,
Pavel