I forgot to memtion an important thing.
Xen needs to change both reference count(count member) and
its page owner(_domain member) atomically.
Some codes depends on the fact that count and _domain are packed in 64bit.
e.g. steal_page().
On Thu, Sep 21, 2006 at 10:34:04AM +0900, Isaku Yamahata wrote:
>
> 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
>
> _______________________________________________
> Xen-ia64-devel mailing list
> Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-ia64-devel
--
yamahata
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