gnttab: miscellaneous fixes - _GTF_* constants name bit positions, so binary arithmetic on them is wrong - gnttab_clear_flag() cannot (on x86 and ia64 at least) simply use clear_bit(), as that may access more than the two bytes that are intended to be accessed Signed-off-by: Jan Beulich --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -397,7 +397,8 @@ static int _set_status_v2(domid_t domid (id != domid) || (!readonly && (flags & GTF_readonly)) ) { - gnttab_clear_flag(_GTF_reading | _GTF_writing, status); + gnttab_clear_flag(_GTF_writing, status); + gnttab_clear_flag(_GTF_reading, status); PIN_FAIL(done, GNTST_general_error, "Unstable flags (%x) or dom (%d). (expected dom %d) " "(r/w: %d)\n", @@ -1716,14 +1717,14 @@ __release_grant_for_copy( under the domain's grant table lock. */ /* Only safe on transitive grants. Even then, note that we don't attempt to drop any pin on the referent grant. */ -static void __fixup_status_for_pin(struct active_grant_entry *act, +static void __fixup_status_for_pin(const struct active_grant_entry *act, uint16_t *status) { if ( !(act->pin & GNTPIN_hstw_mask) ) - *status &= ~_GTF_writing; + *status &= ~GTF_writing; if ( !(act->pin & GNTPIN_hstr_mask) ) - *status &= ~_GTF_reading; + *status &= ~GTF_reading; } /* Grab a frame number from a grant entry and update the flags and pin --- a/xen/include/asm-ia64/grant_table.h +++ b/xen/include/asm-ia64/grant_table.h @@ -5,6 +5,8 @@ #ifndef __ASM_GRANT_TABLE_H__ #define __ASM_GRANT_TABLE_H__ +#include + #define INITIAL_NR_GRANT_FRAMES 1 // for grant map/unmap @@ -82,9 +84,19 @@ int guest_physmap_add_page(struct domain #define gnttab_mark_dirty(d, f) ((void)f) -static inline void gnttab_clear_flag(unsigned long nr, uint16_t *addr) +static inline void gnttab_clear_flag(unsigned int nr, volatile uint16_t *st) { - clear_bit(nr, addr); + /* + * Note that this cannot be clear_bit(), as the access must be + * confined to the specified 2 bytes. + */ + uint16_t mask = ~(1 << nr), old; + CMPXCHG_BUGCHECK_DECL + + do { + CMPXCHG_BUGCHECK(st); + old = *st; + } while (cmpxchg_rel(st, old, old & mask) != old); } #define gnttab_host_mapping_get_page_type(op, ld, rd) \ --- a/xen/include/asm-x86/grant_table.h +++ b/xen/include/asm-x86/grant_table.h @@ -48,9 +48,13 @@ int replace_grant_host_mapping( #define gnttab_mark_dirty(d, f) paging_mark_dirty((d), (f)) -static inline void gnttab_clear_flag(unsigned long nr, uint16_t *addr) +static inline void gnttab_clear_flag(unsigned int nr, uint16_t *st) { - clear_bit(nr, (unsigned long *)addr); + /* + * Note that this cannot be clear_bit(), as the access must be + * confined to the specified 2 bytes. + */ + asm volatile ("lock btrw %1,%0" : "=m" (*st) : "Ir" (nr), "m" (*st)); } /* Foreign mappings of HHVM-guest pages do not modify the type count. */