Re: [Xen-devel] acpidump crashes on some machines

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Aug 23, 2012 at 12:14:56PM +0200, Andre Przywara wrote:
> On 08/17/2012 10:52 PM, Konrad Rzeszutek Wilk wrote:
> >On Thu, Jul 26, 2012 at 03:02:58PM +0200, Andre Przywara wrote:
> >>On 06/30/2012 04:19 AM, Konrad Rzeszutek Wilk wrote:
> >>
> >>Konrad, David,
> >>
> >>back on track for this issue. Thanks for your input, I could do some
> >>more debugging (see below for a refresh):
> >>
> >>It seems like it affects only the first page of the 1:1 mapping. I
> >>didn't have an issues with the last PFN or the page behind it (which
> >>failed properly).
> >>
> >>David, thanks for the hint with varying dom0_mem parameter. I
> >>thought I already checked this, but I did it once again and it
> >>turned out that it is only an issue if dom0_mem is smaller than the
> >>ACPI area, which generates a hole in the memory map. So we have
> >>(simplified)
> >>* 1:1 mapping to 1 MB
> >>* normal mapping till dom0_mem
> >>* unmapped area till ACPI E820 area
> >>* ACPI E820 1:1 mapping
> >>
> >>As far as I could chase it down the 1:1 mapping itself looks OK, I
> >>couldn't find any off-by-one bugs here. So maybe it is code that
> >>later on invalidates areas between the normal guest mapping and the
> >>ACPI mem?
> >
> >I think I found it. Can you try this pls [and if you can't find
> >early_to_phys.. just use the __set_phys_to call]
> 
> Yes, that works. At least after a quick test on my test box. Both
> the test module and acpidump work as expected. If I replace the "<"
> in your patch with the original "<=", I get the warning (and due to
> the "continue" it also works).
> I also successfully tested the minimal fix (just replacing <= with <).
> I will feed it to the testers here to cover more machines.
> 
> Do you want to keep the warnings in (which exceed 80 characters, btw)?

Yes. The new style is to allow any type of printk/WARN etc to be unbroken
and break the 80 characters.

> 
> Thanks a lot and:
> 
> Tested-by: Andre Przywara <andre.przywara@xxxxxxx>

Great. Thx.
> 
> Regards,
> Andre.
> 
> >
> > From ab915d98f321b0fcca1932747c632b5f0f299f55 Mon Sep 17 00:00:00 2001
> >From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >Date: Fri, 17 Aug 2012 16:43:28 -0400
> >Subject: [PATCH] xen/setup: Fix one-off error when adding for-balloon PFNs to
> >  the P2M.
> >
> >When we are finished with return PFNs to the hypervisor, then
> >populate it back, and also mark the E820 MMIO and E820 gaps
> >as IDENTITY_FRAMEs, we then call P2M to set areas that can
> >be used for ballooning. We were off by one, and ended up
> >over-writting a P2M entry that most likely was an IDENTITY_FRAME.
> >For example:
> >
> >1-1 mapping on 40000->40200
> >1-1 mapping on bc558->bc5ac
> >1-1 mapping on bc5b4->bc8c5
> >1-1 mapping on bc8c6->bcb7c
> >1-1 mapping on bcd00->100000
> >Released 614 pages of unused memory
> >Set 277889 page(s) to 1-1 mapping
> >Populating 40200-40466 pfn range: 614 pages added
> >
> >=> here we set from 40466 up to bc559 P2M tree to be
> >INVALID_P2M_ENTRY. We should have done it up to bc558.
> >
> >The end result is that if anybody is trying to construct
> >a PTE for PFN bc558 they end up with ~PAGE_PRESENT.
> >
> >CC: stable@xxxxxxxxxxxxxxx
> >Reported-by: Andre Przywara <andre.przywara@xxxxxxx>
> >Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >---
> >  arch/x86/xen/setup.c |   11 +++++++++--
> >  1 files changed, 9 insertions(+), 2 deletions(-)
> >
> >diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> >index ead8557..030a55a 100644
> >--- a/arch/x86/xen/setup.c
> >+++ b/arch/x86/xen/setup.c
> >@@ -78,9 +78,16 @@ static void __init xen_add_extra_mem(u64 start, u64 size)
> >     memblock_reserve(start, size);
> >
> >     xen_max_p2m_pfn = PFN_DOWN(start + size);
> >+    for (pfn = PFN_DOWN(start); pfn < xen_max_p2m_pfn; pfn++) {
> >+            unsigned long mfn = pfn_to_mfn(pfn);
> >+
> >+            if (WARN(mfn == pfn, "Trying to over-write 1-1 mapping (pfn: 
> >%lx)\n", pfn))
> >+                    continue;
> >+            WARN(mfn != INVALID_P2M_ENTRY, "Trying to remove %lx which has 
> >%lx mfn!\n",
> >+                    pfn, mfn);
> >
> >-    for (pfn = PFN_DOWN(start); pfn <= xen_max_p2m_pfn; pfn++)
> >-            __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> >+            early_set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> >+    }
> >  }
> >
> >  static unsigned long __init xen_do_chunk(unsigned long start,
> >
> 
> -- 
> Andre Przywara
> AMD-Operating System Research Center (OSRC), Dresden, Germany

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