Re: Re: PATCH] support vmcores with 64k page sizeon 4kpage size kernels

["Sachin P. Sant" <sachinp@xxxxxxxxxx>]

Dave Anderson wrote:
> Haren Myneni wrote:
>
>   
> > Dave Anderson wrote:
> >
> >     
> > > Dave Anderson wrote:
> > >
> > >       
> > > > "Sachin P. Sant" wrote:
> > > >
> > > >         
> > > > > Hi Dave
> > > > > Recently there were changes made to kexec tools to support 64K page
> > > > >           
> > > > size.
> > > >         
> > > > > With those changes vmcore file obtained from a kernel which
> > > > >           
> > > > supports 64K
> > > >         
> > > > > page size cannot be analyzed using crash on a machine running with
> > > > >           
> > > > kernel
> > > >         
> > > > > supporting 4K page size.
> > > > >
> > > > > The following changes in crash tool resolves the problem.
> > > > > Look if the symbol __hash_page_64k exists. This symbol is defined only
> > > > > for kernels with 64K PAGE SIZE support. If yes then the dump was taken
> > > > > with a kernel supporting 64k page size. So use the vmcore page
> > > > >           
> > > > size[64K]
> > > >         
> > > > > instead of getpagesize().
> > > > >
> > > > > Thanks
> > > > > -Sachin
> > > > >
> > > > >
> > > > >           
> > > > ------------------------------------------------------------------------------------------------------------------------
> > > >
> > > >         
> > > > > * Recently there were changes made to kexec tools to support 64K
> > > > >           
> > > > page size.
> > > >         
> > > > >   With those changes vmcore file obtained from a kernel which
> > > > >           
> > > > supports 64K
> > > >         
> > > > >   page size cannot be analyzed using crash on a machine running
> > > > >           
> > > > with kernel
> > > >         
> > > > >   supporting 4K page size.
> > > > >   The following change were made in crash tool to solve the problem.
> > > > >   Look if the symbol __hash_page_64k exists. If yes then the dump
> > > > >           
> > > > was taken
> > > >         
> > > > >   with a kernel supporting 64k page size. So change the page size
> > > > >           
> > > > accordingly.
> > > >         
> > > > > Signed-Off-By: Sachin Sant <sachinp@xxxxxxxxxx>
> > > > > --
> > > > >
> > > > > diff -Naurp crash-4.0/defs.h crash-4.0-new/defs.h
> > > > > --- crash-4.0/defs.h    2006-09-14 21:41:50.000000000 -0400
> > > > > +++ crash-4.0-new/defs.h        2006-09-14 21:48:37.000000000 -0400
> > > > > @@ -2297,6 +2297,7 @@ struct efi_memory_desc_t {
> > > > >  #define _64BIT_
> > > > >  #define MACHINE_TYPE       "PPC64"
> > > > >
> > > > > +#define PPC64_64K_PAGE_SIZE    65536
> > > > >  #define PAGEBASE(X)  (((ulong)(X)) & (ulong)machdep->pagemask)
> > > > >
> > > > >  #define PTOV(X)            ((unsigned long)(X)+(machdep->kvbase))
> > > > > diff -Naurp crash-4.0/ppc64.c crash-4.0-new/ppc64.c
> > > > > --- crash-4.0/ppc64.c   2006-09-14 21:41:50.000000000 -0400
> > > > > +++ crash-4.0-new/ppc64.c       2006-09-14 21:50:26.000000000 -0400
> > > > > @@ -67,19 +67,6 @@ ppc64_init(int when)
> > > > >                 machdep->verify_symbol = ppc64_verify_symbol;
> > > > >                 if (pc->flags & KERNEL_DEBUG_QUERY)
> > > > >                         return;
> > > > > -               machdep->pagesize = memory_page_size();
> > > > > -               machdep->pageshift = ffs(machdep->pagesize) - 1;
> > > > > -               machdep->pageoffset = machdep->pagesize - 1;
> > > > > -               machdep->pagemask = ~((ulonglong)machdep->pageoffset);
> > > > > -               machdep->stacksize = 4 * machdep->pagesize;
> > > > > -               if ((machdep->pgd = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > -                       error(FATAL, "cannot malloc pgd space.");
> > > > > -               if ((machdep->pmd = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > -                       error(FATAL, "cannot malloc pmd space.");
> > > > > -               if ((machdep->ptbl = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > -                       error(FATAL, "cannot malloc ptbl space.");
> > > > > -               if ((machdep->machspec->level4 = (char
> > > > >           
> > > > *)malloc(PAGESIZE())) == NULL)
> > > >         
> > > > > -                       error(FATAL, "cannot malloc level4 space.");
> > > > >                 machdep->last_pgd_read = 0;
> > > > >                  machdep->last_pmd_read = 0;
> > > > >                  machdep->last_ptbl_read = 0;
> > > > > @@ -93,6 +80,40 @@ ppc64_init(int when)
> > > > >                 break;
> > > > >
> > > > >         case PRE_GDB:
> > > > > +               /*
> > > > > +                * Recently there were changes made to kexec tools
> > > > > +                * to support 64K page size. With those changes
> > > > > +                * vmcore file obtained from a kernel which supports
> > > > > +                * 64K page size cannot be analyzed using crash on a
> > > > > +                * machine running with kernel supporting 4K page size
> > > > > +                *
> > > > > +                * The following modifications are required in crash
> > > > > +                * tool to be in sync with kexec tools.
> > > > > +                *
> > > > > +                * Look if the following symbol exists. If yes then
> > > > > +                * the dump was taken with a kernel supporting 64k
> > > > > +                * page size. So change the page size accordingly.
> > > > > +                *
> > > > > +                * Also moved the following code block from
> > > > > +                * PRE_SYMTAB case here.
> > > > > +                */
> > > > > +                if (symbol_exists("__hash_page_64K"))
> > > > > +                        machdep->pagesize = PPC64_64K_PAGE_SIZE;
> > > > > +                else
> > > > > +                       machdep->pagesize = memory_page_size();
> > > > > +               machdep->pageshift = ffs(machdep->pagesize) - 1;
> > > > > +               machdep->pageoffset = machdep->pagesize - 1;
> > > > > +               machdep->pagemask = ~((ulonglong)machdep->pageoffset);
> > > > > +               machdep->stacksize = 4 * machdep->pagesize;
> > > > > +               if ((machdep->pgd = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > +                       error(FATAL, "cannot malloc pgd space.");
> > > > > +               if ((machdep->pmd = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > +                       error(FATAL, "cannot malloc pmd space.");
> > > > > +               if ((machdep->ptbl = (char *)malloc(PAGESIZE())) ==
> > > > >           
> > > > NULL)
> > > >         
> > > > > +                       error(FATAL, "cannot malloc ptbl space.");
> > > > > +               if ((machdep->machspec->level4 = (char
> > > > >           
> > > > *)malloc(PAGESIZE())) == NULL)
> > > >         
> > > > > +                       error(FATAL, "cannot malloc level4 space.");
> > > > > +
> > > > >                 machdep->kvbase = symbol_value("_stext");
> > > > >                 machdep->identity_map_base = machdep->kvbase;
> > > > >                  machdep->is_kvaddr = generic_is_kvaddr;
> > > > >           
> > > > The patch looks safe enough.
> > > >
> > > > A couple things I just noticed though...
> > > >
> > > > Is it true that the process stack size will be 256K?  And the
> > > > ppc64 hardware interrupt stack would be 512K?  Based upon
> > > > the machdep->pagesize value, these inititializations get done
> > > > later:
> > > >
> > > >    machdep->stacksize = 4 * machdep->pagesize;
> > > >
> > > >    machdep->machspec->hwstacksize = 8 * machdep->pagesize;
> > > >
> > > > If they have not increased, won't the backtrace code get confused?
> > > >
> > > > Thanks,
> > > >   Dave
> > > >
> > > >         
> > > The kernel's asm-powerpc/thread_info.h file doesn't
> > > show any change in stack size, which I didn't expect
> > > it would anyway:
> > >
> > >   #ifdef __KERNEL__
> > >
> > >   /* We have 8k stacks on ppc32 and 16k on ppc64 */
> > >
> > >   #ifdef CONFIG_PPC64
> > >   #define THREAD_SHIFT            14
> > >   #else
> > >   #define THREAD_SHIFT            13
> > >   #endif
> > >
> > >   #define THREAD_SIZE             (1 << THREAD_SHIFT)
> > >
> > > and the hardware interrupt stack seems to only be in
> > > the paca_struct in 2.4 kernels.
> > >
> > > I think we can safely hardwire those two values anyway,
> > > right?
> > >
> > >       
> > Sachin, Yes, we should be hardcoding the stack size value (16K). It does
> > not matter for hardware intr stack which is used only for 2.4 kernel and
> > supports only 4K page. Uses soft IRQ and hard IRQ stacks in 2.6 kernel
> > for interrupt context and their sizes are the same as THREAD_SIZE.
> >
> > This patch should also support backward compatibility since the symbol
> > __hash_page_64K does not exist and thus the page size is always 4K.
> >
> >     
>
> Thanks, Haren.  Sachin is probably blissfully asleep and not aware of
> this discussion, so I will go ahead and modify his patch to:
>
> (1) hardwire the process stack size, and
> (2) as you state, it doesn't really make a difference for the 2.4 kernel
>     since it won't ever see the larger pagesize.
>   
Thanks Haren, Dave . I was travelling back to india, so missed this part 
of the
discussion. 

> Thanks,
>   Dave
>
>
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