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

[Andre Przywara <andre.przywara@xxxxxxx>]

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)?

Thanks a lot and:

Tested-by: Andre Przywara <andre.przywara@xxxxxxx>

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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