Re: [Xen-ia64-devel] [patch] alloc_page_dir() should return a virtual address

[Kouya SHIMURA <kouya@xxxxxxxxxxxxxx>]

Hi Jes,

I wrote the patch corresponding to discontig. You are wrong.
alloc_dir_page() must return a physical address because the page table
walker for frame_table runs under off-state of data-address-translation.
(i.e. psr.dt=0)

p*d_populate() functions never be called while handling TLB miss to
frame_table. The page table walker for frame_table is written in
assembler in xen/arch/ia64/xen/ivt.S. See the code between
'GLOBAL_ENTRY(frametable_miss)' and 'END(frametable_miss)'

You'd better have a look at the thread below:
http://lists.xensource.com/archives/html/xen-ia64-devel/2006-04/msg00014.html

Thanks,
Kouya

Jes Sorensen writes:
 > Hi,
 > 
 > I sent this patch to Alex last week, but it didn't make it onto the list
 > because it's wrongly configured, so here we go again.
 > 
 > I know that this patch is causing problems on ZX1, but I have looked at
 > it over and over again and I feel pretty certain it is correct. In fact
 > I cannot understand that Xen could boot on any ia64 platform prior to
 > this at all.
 > 
 > I would be very interested in hearing how this patch affects other
 > platforms such as DIG and Fujitsu's machines (if they are not DIG :)
 > 
 > Any input or comments on this is most welcome - if you think I am wrong
 > about this patch, please tell me, I really want to understand why this
 > worked in the past.
 > 
 > Thanks,
 > Jes
 > 
 > alloc_dir_page() must return a virtual address so it can handle being
 > passed to the p*d_populate() functions which do a __pa() on the address
 > before sticking them into the page tables.
 > 
 > To match this it is also necessary to correctly check the faulting
 > address for being in the virtual frame table range, otherwise page
 > faults for this space weren't being served at all.
 > 
 > This could probably be done more efficiently, but for now I think it's
 > better to keep the code explicit.
 > 
 > Signed-off-by: Jes Sorensen <jes@xxxxxxx>
 > 
 > diff -r 3e4fa8b5b245 xen/arch/ia64/xen/ivt.S
 > --- a/xen/arch/ia64/xen/ivt.S        Tue Sep 12 11:43:22 2006 -0600
 > +++ b/xen/arch/ia64/xen/ivt.S        Wed Sep 20 14:56:37 2006 +0200
 > @@ -542,8 +542,16 @@ late_alt_dtlb_miss:
 >      ;;
 >  #ifdef CONFIG_VIRTUAL_FRAME_TABLE
 >      shr r22=r16,56          // Test for the address of virtual frame_table
 > +#if 1
 > +    mov r23=VIRT_FRAME_TABLE_ADDR>>56
 > +    ;;
 > +    xor r23=r22,r23
 > +    ;;
 > +    cmp.eq p8,p0=r23,r0
 > +#else
 >      ;;
 >      cmp.eq p8,p0=((VIRT_FRAME_TABLE_ADDR>>56)&0xff)-0x100,r22
 > +#endif
 >  (p8)        br.cond.sptk frametable_miss ;;
 >  #endif
 >      // If it is not a Xen address, handle it via page_fault.
 > diff -r 3e4fa8b5b245 xen/arch/ia64/xen/xenmem.c
 > --- a/xen/arch/ia64/xen/xenmem.c     Tue Sep 12 11:43:22 2006 -0600
 > +++ b/xen/arch/ia64/xen/xenmem.c     Wed Sep 20 17:14:01 2006 +0200
 > @@ -76,13 +76,13 @@ alloc_dir_page(void)
 >  alloc_dir_page(void)
 >  {
 >      unsigned long mfn = alloc_boot_pages(1, 1);
 > -    unsigned long dir;
 > +    unsigned char *virtual;
 >      if (!mfn)
 >              panic("Not enough memory for virtual frame table!\n");
 >      ++table_size;
 > -    dir = mfn << PAGE_SHIFT;
 > -    memset(__va(dir), 0, PAGE_SIZE);
 > -    return (void *)dir;
 > +    virtual = __va(mfn << PAGE_SHIFT);
 > +    memset(virtual, 0, PAGE_SIZE);
 > +    return virtual;
 >  }
 >  
 >  static inline unsigned long
 > _______________________________________________
 > Xen-ia64-devel mailing list
 > Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
 > http://lists.xensource.com/xen-ia64-devel


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