On Fri, Jan 14, 2022 at 05:15:35PM +0800, Jason Wang wrote: > > 在 2022/1/14 上午10:32, Jason Wang 写道: > > > > dressSpace *as) > > > > /* GHashTable functions */ > > > > static gboolean vtd_uint64_equal(gconstpointer v1, gconstpointer v2) > > > > { > > > > - return *((const uint64_t *)v1) == *((const uint64_t *)v2); > > > > + const struct vtd_as_key *key1 = v1; > > > > + const struct vtd_as_key *key2 = v2; > > > > + > > > > + return (key1->bus == key2->bus) && (key1->devfn == key2->devfn); > > > > } > > > > static guint vtd_uint64_hash(gconstpointer v) > > > > { > > > > - return (guint)*(const uint64_t *)v; > > > > + const struct vtd_as_key *key = v; > > > > + guint value = (guint)(uintptr_t)key->bus; > > > > + > > > > + return (guint)(value << 8 | key->devfn); > > > Note that value is a pointer to PCIBus*. Just want to check with > > > you that it's > > > intended to use this hash value (or maybe you wanted to use Source > > > ID so it is > > > bus number to use not the bus pointer)? > > > > > > Right, SID should be used here. > > > Sorry for taking too long for the context switching ... > > The hash and shift based the bus pointer is intended since we use bus > pointer as part of the key. The reason is still, during vtd_find_add_as(), > SID is not correct since guest might not finish the initialization of the > device and PCI bridge.
Ah, right. However here value is left-shifted 8 bits so I'm not sure how it could guarantee no collision - logically any addresses that match lower 56 bits will hit with the same devfn by accident. I don't think it'll matter in reality, but... wondering whether it's easier to simply use g_direct_hash() (the glibc provided hash function when hash==NULL is passed over, IOW we simply pass hash_func=NULL for g_hash_table_new) so we'll hash with struct vtd_as_key* instead; IMHO that'll suffice too. Thanks, -- Peter Xu