Re: [Xen-devel] [xen-unstable test] 64494: regressions - FAIL

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Nov 19, 2015 at 12:47:41PM +0100, Juergen Gross wrote:
> On 19/11/15 11:30, Ian Campbell wrote:
> > On Thu, 2015-11-19 at 11:24 +0100, Juergen Gross wrote:
> >> On 18/11/15 15:49, Wei Liu wrote:
> >>> Hi Juergen
> >>>
> >>> Looks like there is something we missed after all.
> >>>
> >>> On Wed, Nov 18, 2015 at 02:31:57PM +0000, osstest service owner wrote:
> >>>> flight 64494 xen-unstable real [real]
> >>>> http://logs.test-lab.xenproject.org/osstest/logs/64494/
> >>>>
> >>>> Regressions :-(
> >>>>
> >>>> Tests which did not succeed and are blocking,
> >>>> including tests which could not be run:
> >>>
> >>>>  test-amd64-amd64-i386-pvgrub 10 guest-start               fail REGR.
> >>>> vs. 64035
> >>>
> >>> Nov 18 05:11:19.753014 (d2) Bootstrapping...
> >>> Nov 18 05:11:19.769108 (d2) Xen Minimal OS!
> >>> Nov 18 05:11:19.769134 (d2)   start_info: 0xa13000(VA)
> >>> Nov 18 05:11:19.769158 (d2)     nr_pages: 0x20000
> >>> Nov 18 05:11:19.777046 (d2)   shared_inf: 0xca1fc000(MA)
> >>> Nov 18 05:11:19.777072 (d2)      pt_base: 0xa16000(VA)
> >>> Nov 18 05:11:19.785042 (d2) nr_pt_frames: 0xb
> >>> Nov 18 05:11:19.785077 (d2)     mfn_list: 0x993000(VA)
> >>> Nov 18 05:11:19.785108 (d2)    mod_start: 0x0(VA)
> >>> Nov 18 05:11:19.785135 (d2)      mod_len: 0
> >>> Nov 18 05:11:19.793047 (d2)        flags: 0x0
> >>> Nov 18 05:11:19.793077 (d2)     cmd_line: (hd0,0)/boot/grub/menu.lst
> >>> Nov 18 05:11:19.793108 (d2)        stack: 0x972580-0x992580
> >>> Nov 18 05:11:19.801150 (d2) MM: Init
> >>> Nov 18 05:11:19.801181 (d2)       _text: 0x0(VA)
> >>> Nov 18 05:11:19.801197 (d2)      _etext: 0x7b22d(VA)
> >>> Nov 18 05:11:19.809104 (d2)    _erodata: 0xa4000(VA)
> >>> Nov 18 05:11:19.809123 (d2)      _edata: 0xa81a8(VA)
> >>> Nov 18 05:11:19.809138 (d2) stack start: 0x972580(VA)
> >>> Nov 18 05:11:19.817062 (d2)        _end: 0x992b30(VA)
> >>> Nov 18 05:11:19.817099 (d2)   start_pfn: a24
> >>> Nov 18 05:11:19.817125 (d2)     max_pfn: 20000
> >>> Nov 18 05:11:19.825037 (d2) Mapping memory range 0x1000000 - 0x20000000
> >>> Nov 18 05:11:19.825071 (d2) setting 0x0-0xa4000 readonly
> >>> Nov 18 05:11:19.825100 (d2) skipped 1000
> >>> Nov 18 05:11:19.833049 (d2) MM: Initialise page allocator for
> >>> b1c000(b1c000)-20000000(20000000)
> >>> Nov 18 05:11:19.833089 (d2) Page fault at linear address c00008, eip
> >>> 5fc70, regs 0x98ff28, sp b1c000, our_sp 0x98fefc, code 2
> >>> Nov 18 05:11:19.849044 (d2) Page fault in pagetable walk (access to
> >>> invalid memory?).
> >>>
> >>> The pvgrub in used is 32 bit. 64 bit (which I myself tested) seemed to
> >>> be working fine.
> >>
> >> Okay, I'm hitting this issue, too. I'll investigate further.
> > 
> > Do we want to revert $something in the meantime? If so, what...
> > 
> 
> The problem is really located in pvgrub:
> 

To be precise, the problem is in mini-os, which is used by rump kernel
as well. :-(

> pvgrub is making assumptions about the page table allocation scheme
> of the toolset starting pvgrub. It is calculating the first not yet
> mapped pfn by:
> 
> pfn_to_map =
>     (start_info.nr_pt_frames - NOT_L1_FRAMES) * L1_PAGETABLE_ENTRIES;
> 
> NOT_L1_FRAMES is 3 for 64 bit and 32 bit:
> 
> 64 bit: 1 level 4 + 1 level 4 + 1 level 2
> 32 bit: 1 level 3 + 2 level 2 (assuming level 2 pt are allocated
>   for the first and the last GB)
> 
> This is wrong now, as for 32 bit I'm allocating all level 2 page
> tables from the lowest needed address up to 0xffffffff, resulting
> in 4 level 2 page tables in pvgrub case.
> 
> Setting NOT_L1_FRAMES to 5 for 32 bit pvgrub makes the system boot
> again.
> 
> I think it is wrong for pvgrub to assume a fixed allocation scheme
> of the page tables. The question is how to fix it: either via
> changing NOT_L1_FRAMES or by doing it in a clean but more complicated
> way.
> 

In the mean time, shall we revert the series and think about this a bit
more?

How complicated will be clean fix be?

Does changing NOT_L1_FRAMES break mini-os boot with toolstack prior to
your series?

Wei.

> 
> Juergen
> 

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