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))
> _______________________________________________
> Xen-ia64-devel mailing list
> Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-ia64-devel
--
yamahata
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