[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 2 of 3] Ensure liveness of pages involved in a guest page table walk
xen/arch/x86/mm/guest_walk.c | 16 +++++++++++----- 1 files changed, 11 insertions(+), 5 deletions(-) Instead of risking deadlock by holding onto the gfn's acquired during a guest page table walk, acquire an extra reference within the get_gfn/ put_gfn critical section, and drop the extra reference when done with the map. This ensures liveness of the map, i.e. the underlying page won't be paged out. Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx> diff -r f079cbeae77e -r b0410cb27d17 xen/arch/x86/mm/guest_walk.c --- a/xen/arch/x86/mm/guest_walk.c +++ b/xen/arch/x86/mm/guest_walk.c @@ -87,7 +87,7 @@ static uint32_t set_ad_bits(void *guest_ } /* If the map is non-NULL, we leave this function having - * called get_gfn, you need to call put_gfn. */ + * acquired an extra ref on mfn_to_page(*mfn) */ static inline void *map_domain_gfn(struct p2m_domain *p2m, gfn_t gfn, mfn_t *mfn, @@ -95,6 +95,7 @@ static inline void *map_domain_gfn(struc uint32_t *rc) { p2m_access_t p2ma; + void *map; /* Translate the gfn, unsharing if shared */ *mfn = get_gfn_type_access(p2m, gfn_x(gfn), p2mt, &p2ma, p2m_unshare, NULL); @@ -120,7 +121,12 @@ static inline void *map_domain_gfn(struc } ASSERT(mfn_valid(mfn_x(*mfn))); - return map_domain_page(mfn_x(*mfn)); + /* Get an extra ref to the page to ensure liveness of the map. + * Then we can safely put gfn */ + page_get_owner_and_reference(mfn_to_page(mfn_x(*mfn))); + map = map_domain_page(mfn_x(*mfn)); + __put_gfn(p2m, gfn_x(gfn)); + return map; } @@ -357,20 +363,20 @@ set_ad: if ( l3p ) { unmap_domain_page(l3p); - __put_gfn(p2m, gfn_x(guest_l4e_get_gfn(gw->l4e))); + put_page(mfn_to_page(mfn_x(gw->l3mfn))); } #endif #if GUEST_PAGING_LEVELS >= 3 if ( l2p ) { unmap_domain_page(l2p); - __put_gfn(p2m, gfn_x(guest_l3e_get_gfn(gw->l3e))); + put_page(mfn_to_page(mfn_x(gw->l2mfn))); } #endif if ( l1p ) { unmap_domain_page(l1p); - __put_gfn(p2m, gfn_x(guest_l2e_get_gfn(gw->l2e))); + put_page(mfn_to_page(mfn_x(gw->l1mfn))); } return rc; _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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