[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2 of 3] Make p2m lookups fully synchronized wrt modifications
At 16:42 -0500 on 08 Nov (1320770545), Andres Lagar-Cavilla wrote: > xen/arch/x86/mm/mm-locks.h | 13 +++++++------ > xen/arch/x86/mm/p2m.c | 18 +++++++++++++++++- > xen/include/asm-x86/p2m.h | 39 ++++++++++++++++++++++++--------------- > 3 files changed, 48 insertions(+), 22 deletions(-) > > > We achieve this by locking/unlocking the global p2m_lock in get/put_gfn. > This brings about a few consequences for the p2m_lock: > > - not ordered anymore in mm-locks.h: unshare does get_gfn -> shr_lock, > there are code paths that do paging_lock -> get_gfn. All of these > would cause mm-locks.h to panic. In that case there's a potential deadlock in the sharing code, and turning off the safety catches is not an acceptable response to that. :) ISTR you had a plan to get rid of the shr_lock entirely, or am I misremembering? Tim. > - the lock is always taken recursively, as there are many paths that > do get_gfn -> p2m_lock > > Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx> > > diff -r a0c55cc5d696 -r 6203a0549d8a xen/arch/x86/mm/mm-locks.h > --- a/xen/arch/x86/mm/mm-locks.h > +++ b/xen/arch/x86/mm/mm-locks.h > @@ -165,14 +165,15 @@ declare_mm_lock(nestedp2m) > > /* P2M lock (per-p2m-table) > * > - * This protects all updates to the p2m table. Updates are expected to > - * be safe against concurrent reads, which do *not* require the lock. */ > + * This protects all queries and updates to the p2m table. Because queries > + * can happen interleaved with other locks in here, we do not enforce > + * ordering, and make all locking recursive. */ > > -declare_mm_lock(p2m) > -#define p2m_lock(p) mm_lock(p2m, &(p)->lock) > -#define p2m_lock_recursive(p) mm_lock_recursive(p2m, &(p)->lock) > -#define p2m_unlock(p) mm_unlock(&(p)->lock) > +#define p2m_lock(p) spin_lock_recursive(&(p)->lock.lock) > +#define p2m_lock_recursive(p) spin_lock_recursive(&(p)->lock.lock) > +#define p2m_unlock(p) spin_unlock_recursive(&(p)->lock.lock) > #define p2m_locked_by_me(p) mm_locked_by_me(&(p)->lock) > +#define gfn_locked_by_me(p,g) mm_locked_by_me(&(p)->lock) > > /* Page alloc lock (per-domain) > * > diff -r a0c55cc5d696 -r 6203a0549d8a xen/arch/x86/mm/p2m.c > --- a/xen/arch/x86/mm/p2m.c > +++ b/xen/arch/x86/mm/p2m.c > @@ -158,6 +158,9 @@ mfn_t gfn_to_mfn_type_p2m(struct p2m_dom > return _mfn(gfn); > } > > + /* Grab the lock here, don't release until put_gfn */ > + p2m_lock(p2m); > + > mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order); > > #ifdef __x86_64__ > @@ -182,6 +185,19 @@ mfn_t gfn_to_mfn_type_p2m(struct p2m_dom > return mfn; > } > > +void put_gfn(struct domain *d, unsigned long gfn) > +{ > + struct p2m_domain *p2m = p2m_get_hostp2m(d); > + > + if ( !p2m || !paging_mode_translate(d) ) > + /* Nothing to do in this case */ > + return; > + > + ASSERT(p2m_locked_by_me(p2m)); > + > + p2m_unlock(p2m); > +} > + > int set_p2m_entry(struct p2m_domain *p2m, unsigned long gfn, mfn_t mfn, > unsigned int page_order, p2m_type_t p2mt, p2m_access_t > p2ma) > { > @@ -190,7 +206,7 @@ int set_p2m_entry(struct p2m_domain *p2m > unsigned int order; > int rc = 1; > > - ASSERT(p2m_locked_by_me(p2m)); > + ASSERT(gfn_locked_by_me(p2m, gfn)); > > while ( todo ) > { > diff -r a0c55cc5d696 -r 6203a0549d8a xen/include/asm-x86/p2m.h > --- a/xen/include/asm-x86/p2m.h > +++ b/xen/include/asm-x86/p2m.h > @@ -305,9 +305,10 @@ struct p2m_domain *p2m_get_p2m(struct vc > > #define p2m_get_pagetable(p2m) ((p2m)->phys_table) > > -/**** p2m query accessors. After calling any of the variants below, you > - * need to call put_gfn(domain, gfn). If you don't, you'll lock the > - * hypervisor. ****/ > +/**** p2m query accessors. They lock p2m_lock, and thus serialize > + * lookups wrt modifications. They _do not_ release the lock on exit. > + * After calling any of the variants below, caller needs to use > + * put_gfn. ****/ > > /* Read a particular P2M table, mapping pages as we go. Most callers > * should _not_ call this directly; use the other get_gfn* functions > @@ -349,19 +350,27 @@ static inline unsigned long get_gfn_unty > return INVALID_MFN; > } > > -/* This is a noop for now. */ > -static inline void put_gfn(struct domain *d, unsigned long gfn) > -{ > -} > +/* Will release the p2m_lock and put the page behind this mapping. */ > +void put_gfn(struct domain *d, unsigned long gfn); > > -/* These are identical for now. The intent is to have the caller not worry > - * about put_gfn. To only be used in printk's, crash situations, or to > - * peek at a type. You're not holding the p2m entry exclsively after calling > - * this. */ > -#define get_gfn_unlocked(d, g, t) get_gfn_type((d), (g), (t), > p2m_alloc) > -#define get_gfn_query_unlocked(d, g, t) get_gfn_type((d), (g), (t), > p2m_query) > -#define get_gfn_guest_unlocked(d, g, t) get_gfn_type((d), (g), (t), > p2m_guest) > -#define get_gfn_unshare_unlocked(d, g, t) get_gfn_type((d), (g), (t), > p2m_unshare) > +/* The intent is to have the caller not worry about put_gfn. They apply to > + * very specific situations: debug printk's, dumps during a domain crash, > + * or to peek at a p2m entry/type. Caller is not holding the p2m entry > + * exclusively after calling this. */ > +#define build_unlocked_accessor(name) \ > + static inline mfn_t get_gfn ## name ## _unlocked(struct domain *d, \ > + unsigned long gfn, \ > + p2m_type_t *t) \ > + { \ > + mfn_t mfn = get_gfn ##name (d, gfn, t); \ > + put_gfn(d, gfn); \ > + return mfn; \ > + } > + > +build_unlocked_accessor() > +build_unlocked_accessor(_query) > +build_unlocked_accessor(_guest) > +build_unlocked_accessor(_unshare) > > /* General conversion function from mfn to gfn */ > static inline unsigned long mfn_to_gfn(struct domain *d, mfn_t mfn) > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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