Re: [Xen-devel] [BISECTED] Linux 3.12.7 introduces page map handling regression

[Steven Noonan <steven@xxxxxxxxxxxxxx>]

On Thu, Jan 23, 2014 at 11:23:37AM -0500, Elena Ufimtseva wrote:
> On Wed, Jan 22, 2014 at 3:33 PM, Steven Noonan <steven@xxxxxxxxxxxxxx> wrote:
> > On Wed, Jan 22, 2014 at 03:18:50PM -0500, Elena Ufimtseva wrote:
> >> On Wed, Jan 22, 2014 at 9:29 AM, Daniel Borkmann <borkmann@xxxxxxxxxxxxx> 
> >> wrote:
> >> > On 01/22/2014 08:29 AM, Steven Noonan wrote:
> >> >>
> >> >> On Wed, Jan 22, 2014 at 12:02:15AM -0500, Konrad Rzeszutek Wilk wrote:
> >> >>>
> >> >>> On Tue, Jan 21, 2014 at 07:20:45PM -0800, Steven Noonan wrote:
> >> >>>>
> >> >>>> On Tue, Jan 21, 2014 at 06:47:07PM -0800, Linus Torvalds wrote:
> >> >>>>>
> >> >>>>> On Tue, Jan 21, 2014 at 5:49 PM, Greg Kroah-Hartman
> >> >>>>> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >> >>>
> >> >>>
> >> >>> Adding extra folks to the party.
> >> >>>>>>
> >> >>>>>>
> >> >>>>>> Odds are this also shows up in 3.13, right?
> >> >>>>
> >> >>>>
> >> >>>> Reproduced using 3.13 on the PV guest:
> >> >>>>
> >> >>>>         [  368.756763] BUG: Bad page map in process mp
> >> >>>> pte:80000004a67c6165 pmd:e9b706067
> >> >>>>         [  368.756777] page:ffffea001299f180 count:0 mapcount:-1
> >> >>>> mapping:          (null) index:0x0
> >> >>>>         [  368.756781] page flags: 0x2fffff80000014(referenced|dirty)
> >> >>>>         [  368.756786] addr:00007fd1388b7000 vm_flags:00100071
> >> >>>> anon_vma:ffff880e9ba15f80 mapping:          (null) index:7fd1388b7
> >> >>>>         [  368.756792] CPU: 29 PID: 618 Comm: mp Not tainted 
> >> >>>> 3.13.0-ec2
> >> >>>> #1
> >> >>>>         [  368.756795]  ffff880e9b718958 ffff880e9eaf3cc0
> >> >>>> ffffffff814d8748 00007fd1388b7000
> >> >>>>         [  368.756803]  ffff880e9eaf3d08 ffffffff8116d289
> >> >>>> 0000000000000000 0000000000000000
> >> >>>>         [  368.756809]  ffff880e9b7065b8 ffffea001299f180
> >> >>>> 00007fd1388b8000 ffff880e9eaf3e30
> >> >>>>         [  368.756815] Call Trace:
> >> >>>>         [  368.756825]  [<ffffffff814d8748>] dump_stack+0x45/0x56
> >> >>>>         [  368.756833]  [<ffffffff8116d289>] print_bad_pte+0x229/0x250
> >> >>>>         [  368.756837]  [<ffffffff8116eae3>]
> >> >>>> unmap_single_vma+0x583/0x890
> >> >>>>         [  368.756842]  [<ffffffff8116feb5>] unmap_vmas+0x65/0x90
> >> >>>>         [  368.756847]  [<ffffffff81175dac>] unmap_region+0xac/0x120
> >> >>>>         [  368.756852]  [<ffffffff81176379>] ? 
> >> >>>> vma_rb_erase+0x1c9/0x210
> >> >>>>         [  368.756856]  [<ffffffff81177f10>] do_munmap+0x280/0x370
> >> >>>>         [  368.756860]  [<ffffffff81178041>] vm_munmap+0x41/0x60
> >> >>>>         [  368.756864]  [<ffffffff81178f32>] SyS_munmap+0x22/0x30
> >> >>>>         [  368.756869]  [<ffffffff814e70ed>]
> >> >>>> system_call_fastpath+0x1a/0x1f
> >> >>>>         [  368.756872] Disabling lock debugging due to kernel taint
> >> >>>>         [  368.760084] BUG: Bad rss-counter state mm:ffff880e9d079680
> >> >>>> idx:0 val:-1
> >> >>>>         [  368.760091] BUG: Bad rss-counter state mm:ffff880e9d079680
> >> >>>> idx:1 val:1
> >> >>>>
> >> >>>>>
> >> >>>>> Probably. I don't have a Xen PV setup to test with (and very little
> >> >>>>> interest in setting one up).. And I have a suspicion that it might 
> >> >>>>> not
> >> >>>>> be so much about Xen PV, as perhaps about the kind of hardware.
> >> >>>>>
> >> >>>>> I suspect the issue has something to do with the magic _PAGE_NUMA
> >> >>>>> tie-in with _PAGE_PRESENT. And then mprotect(PROT_NONE) ends up
> >> >>>>> removing the _PAGE_PRESENT bit, and now the crazy numa code is
> >> >>>>> confused.
> >> >>>>>
> >> >>>>> The whole _PAGE_NUMA thing is a f*cking horrible hack, and shares the
> >> >>>>> bit with _PAGE_PROTNONE, which is why it then has that tie-in to
> >> >>>>> _PAGE_PRESENT.
> >> >>>>>
> >> >>>>> Adding Andrea to the Cc, because he's the author of that horridness.
> >> >>>>> Putting Steven's test-case here as an attachement for Andrea, maybe
> >> >>>>> that makes him go "Ahh, yes, silly case".
> >> >>>>>
> >> >>>>> Also added Kirill, because he was involved the last _PAGE_NUMA 
> >> >>>>> debacle.
> >> >>>>>
> >> >>>>> Andrea, you can find the thread on lkml, but it boils down to commit
> >> >>>>> 1667918b6483 (backported to 3.12.7 as 3d792d616ba4) breaking the
> >> >>>>> attached test-case (but apparently only under Xen PV). There it
> >> >>>>> apparently causes a "BUG: Bad page map .." error.
> >> >>>
> >> >>>
> >> >>> I *think* it is due to the fact that pmd_numa and pte_numa is getting 
> >> >>> the
> >> >>> _raw_
> >> >>> value of PMDs and PTEs. That is - it does not use the pvops interface
> >> >>> and instead reads the values directly from the page-table. Since the
> >> >>> page-table is also manipulated by the hypervisor - there are certain
> >> >>> flags it also sets to do its business. It might be that it uses
> >> >>> _PAGE_GLOBAL as well - and Linux picks up on that. If it was using
> >> >>> pte_flags that would invoke the pvops interface.
> >> >>>
> >> >>> Elena, Dariof and George, you guys had been looking at this a bit 
> >> >>> deeper
> >> >>> than I have. Does the Xen hypervisor use the _PAGE_GLOBAL for PV 
> >> >>> guests?
> 
> It does use _PAGE_GLOBAL for guest user pages
> 
> >> >>>
> >> >>> This not-compiled-totally-bad-patch might shed some light on what I was
> >> >>> thinking _could_ fix this issue - and IS NOT A FIX - JUST A HACK.
> >> >>> It does not fix it for PMDs naturally (as there are no PMD paravirt ops
> >> >>> for that).
> >> >>
> >> >>
> >> >> Unfortunately the Totally Bad Patch seems to make no difference. I am
> >> >> still able to repro the issue:
> >>
> >> Steven, do you use numa=fake on boot cmd line for pv guest?
> >>
> >> I had similar issue on pv guest. Let me check if the fix that resolved
> >> this for me will help with 3.13.
> >
> > Nope:
> >
> > # cat /proc/cmdline
> > root=/dev/xvda1 ro rootwait rootfstype=ext4 nomodeset console=hvc0 
> > earlyprintk=xen,verbose loglevel=7
> 
> >
> >>
> >> >
> >> >
> >> > Maybe this one is also related to this BUG here (cc'ed people 
> >> > investigating
> >> > this one) ...
> >> >
> >> >   https://lkml.org/lkml/2014/1/10/427
> >> >
> >> > ... not sure, though.
> >> >
> >> >
> >> >>         [  346.374929] BUG: Bad page map in process mp
> >> >> pte:80000004ae928065 pmd:e993f9067
> >> >>         [  346.374942] page:ffffea0012ba4a00 count:0 mapcount:-1 
> >> >> mapping:
> >> >> (null) index:0x0
> >> >>         [  346.374946] page flags: 0x2fffff80000014(referenced|dirty)
> >> >>         [  346.374951] addr:00007f06a9bbb000 vm_flags:00100071
> >> >> anon_vma:ffff880e9939fe00 mapping:          (null) index:7f06a9bbb
> >> >>         [  346.374956] CPU: 29 PID: 609 Comm: mp Not tainted 3.13.0-ec2+
> >> >> #1
> >> >>         [  346.374960]  ffff880e9cc38da8 ffff880e991a3cc0 
> >> >> ffffffff814d8768
> >> >> 00007f06a9bbb000
> >> >>         [  346.374967]  ffff880e991a3d08 ffffffff8116d289 
> >> >> 0000000000000000
> >> >> 0000000000000000
> >> >>         [  346.374972]  ffff880e993f9dd8 ffffea0012ba4a00 
> >> >> 00007f06a9bbc000
> >> >> ffff880e991a3e30
> >> >>         [  346.374979] Call Trace:
> >> >>         [  346.374988]  [<ffffffff814d8768>] dump_stack+0x45/0x56
> >> >>         [  346.374996]  [<ffffffff8116d289>] print_bad_pte+0x229/0x250
> >> >>         [  346.375000]  [<ffffffff8116eae3>] 
> >> >> unmap_single_vma+0x583/0x890
> >> >>         [  346.375006]  [<ffffffff8116feb5>] unmap_vmas+0x65/0x90
> >> >>         [  346.375011]  [<ffffffff81175dbc>] unmap_region+0xac/0x120
> >> >>         [  346.375016]  [<ffffffff81176389>] ? vma_rb_erase+0x1c9/0x210
> >> >>         [  346.375021]  [<ffffffff81177f20>] do_munmap+0x280/0x370
> >> >>         [  346.375025]  [<ffffffff81178051>] vm_munmap+0x41/0x60
> >> >>         [  346.375029]  [<ffffffff81178f42>] SyS_munmap+0x22/0x30
> >> >>         [  346.375034]  [<ffffffff814e712d>]
> >> >> system_call_fastpath+0x1a/0x1f
> >> >>         [  346.375037] Disabling lock debugging due to kernel taint
> >> >>         [  346.380082] BUG: Bad rss-counter state mm:ffff880e9d22bc00
> >> >> idx:0 val:-1
> >> >>         [  346.380088] BUG: Bad rss-counter state mm:ffff880e9d22bc00
> >> >> idx:1 val:1
> >> >>
> >> >> This dump doesn't look dramatically different, either.
> >> >>
> >> >>>
> >> >>> The other question is - how is AutoNUMA running when it is not enabled?
> >> >>> Shouldn't those _PAGE_NUMA ops be nops when AutoNUMA hasn't even been
> >> >>> turned on?
> >> >>
> >> >>
> >> >> Well, NUMA_BALANCING is enabled in the kernel config[1], but I presume 
> >> >> you
> >> >> mean not enabled at runtime?
> >> >>
> >> >> [1]
> >> >> http://git.uplinklabs.net/snoonan/projects/archlinux/ec2/ec2-packages.git/tree/linux-ec2/config.x86_64
> >>
> >>
> >>
> >> --
> >> Elena
> 
> I was able to reproduce this consistently, also with the latest mm
> patches from yesterday.
> Can you please try this:
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index ce563be..76dcf96 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -365,7 +365,7 @@ void xen_ptep_modify_prot_commit(struct mm_struct
> *mm, unsigned long addr,
>  /* Assume pteval_t is equivalent to all the other *val_t types. */
>  static pteval_t pte_mfn_to_pfn(pteval_t val)
>  {
> -       if (val & _PAGE_PRESENT) {
> +       if ((val & _PAGE_PRESENT) || ((val &
> (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA)) {
>                 unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
>                 unsigned long pfn = mfn_to_pfn(mfn);
> 
> @@ -381,7 +381,7 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
> 
>  static pteval_t pte_pfn_to_mfn(pteval_t val)
>  {
> -       if (val & _PAGE_PRESENT) {
> +       if ((val & _PAGE_PRESENT) || ((val &
> (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA)) {
>                 unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
>                 pteval_t flags = val & PTE_FLAGS_MASK;
>                 unsigned long mfn;

Thanks Elena, I just tested that and it does un-break things.

- Steven

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