Re: [GIT PULL] x86/mm changes for v3.9-rc1

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Feb 21, 2013 at 04:34:06PM -0800, H. Peter Anvin wrote:
> Hi Linus,
> 
> This is a huge set of several partly interrelated (and concurrently
> developed) changes, which is why the branch history is messier than
> one would like.
> 
> The *really* big items are two humonguous patchsets mostly developed
> by Yinghai Lu at my request, which completely revamps the way we
> create initial page tables.  In particular, rather than estimating how
> much memory we will need for page tables and then build them into that
> memory -- a calculation that has shown to be incredibly fragile -- we
> now build them (on 64 bits) with the aid of a "pseudo-linear mode" --
> a #PF handler which creates temporary page tables on demand.
> 
> This has several advantages:
> 
> 1. It makes it much easier to support things that need access to
>    data very early (a followon patchset uses this to load microcode
>    way early in the kernel startup).
> 
> 2. It allows the kernel and all the kernel data objects to be invoked
>    from above the 4 GB limit.  This allows kdump to work on very large
>    systems.
> 
> 3. It greatly reduces the difference between Xen and native (Xen's
>    equivalent of the #PF handler are the temporary page tables created
>    by the domain builder), eliminating a bunch of fragile hooks.
> 
> The patch series also gets us a bit closer to W^X.
> 
> Additional work in this pull is the 64-bit get_user() work which you
> were also involved with, and a bunch of cleanups/speedups to
> __phys_addr()/__pa().

Looking at figuring out which of the patches in the branch did this, but
with this merge I am getting a crash with a very simple PV guest (booted with
one 1G):

Call Trace:
  [<ffffffff8103feba>] xen_get_user_pgd+0x5a  <--
  [<ffffffff8103feba>] xen_get_user_pgd+0x5a 
  [<ffffffff81042d27>] xen_write_cr3+0x77 
  [<ffffffff81ad2d21>] init_mem_mapping+0x1f9 
  [<ffffffff81ac293f>] setup_arch+0x742 
  [<ffffffff81666d71>] printk+0x48 
  [<ffffffff81abcd62>] start_kernel+0x90 
  [<ffffffff8109416b>] __add_preferred_console.clone.1+0x9b 
  [<ffffffff81abc5f7>] x86_64_start_reservations+0x2a 
  [<ffffffff81abf0c7>] xen_start_kernel+0x564 

And the hypervisor says:
(XEN) d7:v0: unhandled page fault (ec=0000)
(XEN) Pagetable walk from ffffea000005b2d0:
(XEN)  L4[0x1d4] = 0000000000000000 ffffffffffffffff
(XEN) domain_crash_sync called from entry.S
(XEN) Domain 7 (vcpu#0) crashed on cpu#3:
(XEN) ----[ Xen-4.2.0  x86_64  debug=n  Not tainted ]----
(XEN) CPU:    3
(XEN) RIP:    e033:[<ffffffff8103feba>]
(XEN) RFLAGS: 0000000000000206   EM: 1   CONTEXT: pv guest
(XEN) rax: ffffea0000000000   rbx: 0000000001a0c000   rcx: 0000000080000000
(XEN) rdx: 000000000005b2a0   rsi: 0000000001a0c000   rdi: 0000000000000000
(XEN) rbp: ffffffff81a01dd8   rsp: ffffffff81a01d90   r8:  0000000000000000
(XEN) r9:  0000000010000001   r10: 0000000000000000   r11: 0000000000000000
(XEN) r12: 0000000000000000   r13: 0000001000000000   r14: 0000000000000000
(XEN) r15: 0000000000100000   cr0: 000000008005003b   cr4: 00000000000406f0
(XEN) cr3: 0000000411165000   cr2: ffffea000005b2d0
(XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e02b   cs: e033
(XEN) Guest stack trace from rsp=ffffffff81a01d90:
(XEN)    0000000080000000 0000000000000000 0000000000000000 ffffffff8103feba
(XEN)    000000010000e030 0000000000010006 ffffffff81a01dd8 000000000000e02b


What is bizzare is that I do recall testing this (and Stefano also did it).
So I am not sure what has altered.