Re: [Xen-ia64-devel] pickled code

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Hi Jes.

It tries to keep struct page_info compact layout by avoiding
padding before _domain member.
Please notice u32 count_info member in front of _domain.

struct domain is allocated from xen heap,
i.e. the range [PAGE_OFFSET, PAGE_OFFSET + 64MB).
It means that struct domain* can be expressed as
PAGE_OFFSET + 32bit offset(=machine phsyiacal address).

pickle          PAGE_OFFSET + 32bit offset => 32 bit offset
                i.e. discarding most significant 32bit.
                It can be don by casting u64 to u32 because
                Xen assumes little endian.
        
unpickle        32bit offset(=machine phsyical address)
                         => PAGE_OFFSET + 32 bit offset
                i.e. __va()


On Wed, Sep 20, 2006 at 04:21:56PM +0200, Jes Sorensen wrote:
> Hi,
> 
> I found another interesting issue in the code - the way the 'pickle'
> functions work just cannot be right. There is no way one should ever
> try and truncate the output of __pa() to u32 or expect to be able to
> run __va() on a u32 and obtain any level of usable output.
> 
> I have to admit I have zero clue what the pickle code is trying to
> achieve, but I am at least fairly confident that something needs to
> be done in this space :(
> 
> Cheers,
> Jes
> 

> Truncating __va() and __pa() output to u32 is simply not going to work.
> Some platforms don't even have any physical memory within the 4GB window.
> 
> Signed-off-by: Jes Sorensen <jes@xxxxxxx>
> 
> 
> diff -r 3e4fa8b5b245 xen/arch/ia64/xen/mm.c
> --- a/xen/arch/ia64/xen/mm.c  Tue Sep 12 11:43:22 2006 -0600
> +++ b/xen/arch/ia64/xen/mm.c  Wed Sep 20 15:47:09 2006 +0200
> @@ -213,7 +213,7 @@ static void
>  static void
>  try_to_clear_PGC_allocate(struct domain* d, struct page_info* page)
>  {
> -    u32 _d, _nd;
> +    u64 _d, _nd;
>      u64 x, nx, y;
>  
>      _d = pickle_domptr(d);
> @@ -1329,7 +1349,7 @@ steal_page(struct domain *d, struct page
>  #if 0 /* if big endian */
>  # error "implement big endian version of steal_page()"
>  #endif
> -    u32 _d, _nd;
> +    u64 _d, _nd;
>      u64 x, nx, y;
>  
>      if (page_get_owner(page) != d) {
> diff -r 3e4fa8b5b245 xen/include/asm-ia64/mm.h
> --- a/xen/include/asm-ia64/mm.h       Tue Sep 12 11:43:22 2006 -0600
> +++ b/xen/include/asm-ia64/mm.h       Wed Sep 20 14:12:43 2006 +0200
> @@ -53,7 +53,7 @@ struct page_info
>          /* Page is in use: ((count_info & PGC_count_mask) != 0). */
>          struct {
>              /* Owner of this page (NULL if page is anonymous). */
> -            u32 _domain; /* pickled format */
> +            u64 _domain; /* pickled format */
>              /* Type reference count and various PGT_xxx flags and fields. */
>              unsigned long type_info;
>          } __attribute__ ((packed)) inuse;
> @@ -125,10 +125,10 @@ struct page_info
>  #define IS_XEN_HEAP_FRAME(_pfn) ((page_to_maddr(_pfn) < xenheap_phys_end) \
>                                && (page_to_maddr(_pfn) >= xen_pstart))
>  
> -static inline struct domain *unpickle_domptr(u32 _d)
> +static inline struct domain *unpickle_domptr(u64 _d)
>  { return (_d == 0) ? NULL : __va(_d); }
>  static inline u32 pickle_domptr(struct domain *_d)
> -{ return (_d == NULL) ? 0 : (u32)__pa(_d); }
> +{ return (_d == NULL) ? 0 : (u64)__pa(_d); }
>  
>  #define page_get_owner(_p)   (unpickle_domptr((_p)->u.inuse._domain))
>  #define page_set_owner(_p, _d)       ((_p)->u.inuse._domain = 
> pickle_domptr(_d))

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-- 
yamahata

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