> -----Original Message----- > From: Qemu-devel [mailto:[email protected]] On > Behalf Of Peter Xu > Sent: Wednesday, December 14, 2016 11:06 AM > To: Liu, Yi L <[email protected]>; Jason Wang <[email protected]> > Cc: Lan, Tianyu <[email protected]>; Tian, Kevin <[email protected]>; > [email protected]; [email protected]; [email protected]; qemu- > [email protected]; [email protected]; Liu, Yi <[email protected]> > Subject: Re: [Qemu-devel] [RFC PATCH 01/13] intel_iommu: allocate new key when > creating new address space > > On Mon, Dec 12, 2016 at 04:16:50PM +0800, Liu, Yi L wrote: > > On Tue, Dec 06, 2016 at 06:36:16PM +0800, Peter Xu wrote: > > > From: Jason Wang <[email protected]> > > > > > > We use the pointer to stack for key for new address space, this will > > > break hash table searching, fixing by g_malloc() a new key instead. > > > > > > Cc: Michael S. Tsirkin <[email protected]> > > > Cc: Paolo Bonzini <[email protected]> > > > Cc: Richard Henderson <[email protected]> > > > Cc: Eduardo Habkost <[email protected]> > > > Acked-by: Peter Xu <[email protected]> > > > Signed-off-by: Jason Wang <[email protected]> > > > Signed-off-by: Peter Xu <[email protected]> > > > --- > > > hw/i386/intel_iommu.c | 5 +++-- > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c > > > index 708770e..92e4064 100644 > > > --- a/hw/i386/intel_iommu.c > > > +++ b/hw/i386/intel_iommu.c > > > @@ -2426,12 +2426,13 @@ VTDAddressSpace > *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus, int devfn) > > > VTDAddressSpace *vtd_dev_as; > > > > > > if (!vtd_bus) { > > > + uintptr_t *new_key = g_malloc(sizeof(*new_key)); > > > + *new_key = (uintptr_t)bus; > > > /* No corresponding free() */ > > > vtd_bus = g_malloc0(sizeof(VTDBus) + sizeof(VTDAddressSpace *) * > > > \ > > > X86_IOMMU_PCI_DEVFN_MAX); > > > vtd_bus->bus = bus; > > > - key = (uintptr_t)bus; > > > - g_hash_table_insert(s->vtd_as_by_busptr, &key, vtd_bus); > > > + g_hash_table_insert(s->vtd_as_by_busptr, new_key, vtd_bus); > > Hi Peter, > > Your fix seems to answer an issue I encountered back in Oct. The symptom > > is: use > the same bus value to > > searcha previous inserted entry in s->vtd_as_by_busptr, the result is not > > found. > > > > really grt fix. could explain it a bit on why this change would fix the > > issue? > > The old code is doing g_hash_table_insert() with "&key" as the hash > key. However variable "key" is allocated on stack, so it's value might > change after we return from vtd_find_add_as() (stack variables can > only be used inside its functional scope). The patch switched to use > g_malloc0(), that'll use heap memory rather than stack, which is safe. > > (Forwarding this thankfulness to Jason who is the real author of this > fix :-)
Thanks for the explanation, Peter. I see. Then it is sure this really fix what I encountered in Oct. Really a wonderful fix Jason~ > > Thanks, > > -- peterx
