Is: MTRR issue + Xen + memory clipping? Was:Re: Xen not working with stock Debian Wheezy 3.2 kernel on a Core 2 Duo box

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

On Mon, Jul 08, 2013 at 02:16:07PM +0100, Jan Beulich wrote:
> >>> On 08.07.13 at 14:50, Wei Liu <wei.liu2@citrix.com> wrote:
> > On Mon, Jul 08, 2013 at 12:29:02PM +0100, Jan Beulich wrote:
> >> One question of course is where this pretty unusual "unusable"
> >> memory block comes from on that system. Is this block visible the
> >> same way when booting a native kernel, or is this being forced to
> >> "unusable" by Xen?
> > 
> > Vanilla 3.10 + Xen unstable:
> > [    0.000000] Xen: [mem 0x0000000000000000-0x000000000008efff] usable
> > [    0.000000] Xen: [mem 0x000000000008f000-0x00000000000fffff] reserved
> > [    0.000000] Xen: [mem 0x0000000000100000-0x00000000ce699fff] usable
> > [    0.000000] Xen: [mem 0x00000000ce69a000-0x00000000ce6f0fff] ACPI NVS
> > [    0.000000] Xen: [mem 0x00000000ce6f1000-0x00000000cf5fafff] usable
> > [    0.000000] Xen: [mem 0x00000000cf5fb000-0x00000000cf607fff] reserved
> > [    0.000000] Xen: [mem 0x00000000cf608000-0x00000000cf6a4fff] usable
> > [    0.000000] Xen: [mem 0x00000000cf6a5000-0x00000000cf6a9fff] ACPI data
> > [    0.000000] Xen: [mem 0x00000000cf6aa000-0x00000000cf6aafff] usable
> > [    0.000000] Xen: [mem 0x00000000cf6ab000-0x00000000cf6f1fff] ACPI NVS
> > [    0.000000] Xen: [mem 0x00000000cf6f2000-0x00000000cf6fefff] ACPI data
> > [    0.000000] Xen: [mem 0x00000000cf6ff000-0x00000000cf6fffff] usable
> > [    0.000000] Xen: [mem 0x00000000cf700000-0x00000000cfffffff] reserved
> > [    0.000000] Xen: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
> > [    0.000000] Xen: [mem 0x00000000fff00000-0x00000000ffffffff] reserved
> > [    0.000000] Xen: [mem 0x0000000100000000-0x0000000227ffffff] usable
> > [    0.000000] Xen: [mem 0x0000000228000000-0x000000022bffffff] unusable
> > [    0.000000] ERROR: earlyprintk= xenboot already used
> > [    0.000000] NX (Execute Disable) protection: active
> > [    0.000000] SMBIOS 2.4 present.
> > [    0.000000] No AGP bridge found
> > [    0.000000] e820: last_pfn = 0x228000 max_arch_pfn = 0x400000000
> > [    0.000000] e820: last_pfn = 0xcf700 max_arch_pfn = 0x400000000
> > [    0.000000] Scanning 1 areas for low memory corruption
> > [    0.000000] init_memory_mapping: [mem 0x00000000-0x000fffff]
> > [    0.000000] init_memory_mapping: [mem 0x219e00000-0x219ffffff]
> > [    0.000000] init_memory_mapping: [mem 0x218000000-0x219dfffff]
> > [    0.000000] init_memory_mapping: [mem 0x200000000-0x217ffffff]
> > [    0.000000] init_memory_mapping: [mem 0x00100000-0xce699fff]
> > [    0.000000] init_memory_mapping: [mem 0xce6f1000-0xcf5fafff]
> > [    0.000000] init_memory_mapping: [mem 0xcf608000-0xcf6a4fff]
> > [    0.000000] init_memory_mapping: [mem 0xcf6aa000-0xcf6aafff]
> > [    0.000000] init_memory_mapping: [mem 0xcf6ff000-0xcf6fffff]
> > [    0.000000] init_memory_mapping: [mem 0x100000000-0x1ffffffff]
> > [    0.000000] init_memory_mapping: [mem 0x21a000000-0x227ffffff]
> > 
> > We also have the similar unusable block, however the kernel doesn't map it.
> 
> Right, iirc a fix for this was done not too long ago. Konrad may
> recall further details...

Stefan hit this I think. With the MTRR clipping blowing things. CC-ing him
here.
> 
> > 3.2.0-4-amd64 (just found out that there's actually backtrace in dmesg):
> > [    0.000000] BIOS-provided physical RAM map:
> > [    0.000000]  BIOS-e820: 0000000000000000 - 000000000008f000 (usable)
> > [    0.000000]  BIOS-e820: 000000000008f000 - 00000000000a0000 (reserved)
> > [    0.000000]  BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
> > [    0.000000]  BIOS-e820: 0000000000100000 - 00000000ce69a000 (usable)
> > [    0.000000]  BIOS-e820: 00000000ce69a000 - 00000000ce6f1000 (ACPI NVS)
> > [    0.000000]  BIOS-e820: 00000000ce6f1000 - 00000000cf5fb000 (usable)
> > [    0.000000]  BIOS-e820: 00000000cf5fb000 - 00000000cf608000 (reserved)
> > [    0.000000]  BIOS-e820: 00000000cf608000 - 00000000cf6a5000 (usable)
> > [    0.000000]  BIOS-e820: 00000000cf6a5000 - 00000000cf6aa000 (ACPI data)
> > [    0.000000]  BIOS-e820: 00000000cf6aa000 - 00000000cf6ab000 (usable)
> > [    0.000000]  BIOS-e820: 00000000cf6ab000 - 00000000cf6f2000 (ACPI NVS)
> > [    0.000000]  BIOS-e820: 00000000cf6f2000 - 00000000cf6ff000 (ACPI data)
> > [    0.000000]  BIOS-e820: 00000000cf6ff000 - 00000000cf700000 (usable)
> > [    0.000000]  BIOS-e820: 00000000cf700000 - 00000000d0000000 (reserved)
> > [    0.000000]  BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved)
> > [    0.000000]  BIOS-e820: 0000000100000000 - 000000022c000000 (usable)
> 
> So no such block right off the BIOS. You're not using Xen TXT code
> by chance? Off the top of my head I don't recall any other place
> where multiple RAM pages might get turned into "unusable".
> 
> Jan
> 
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