| Message ID | 1481020588-4245-2-git-send-email-peterx@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Dec 06, 2016 at 06:36:16PM +0800, Peter Xu wrote: > From: Jason Wang <jasowang@redhat.com> > > 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 <mst@redhat.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Richard Henderson <rth@twiddle.net> > Cc: Eduardo Habkost <ehabkost@redhat.com> > Acked-by: Peter Xu <peterx@redhat.com> > Signed-off-by: Jason Wang <jasowang@redhat.com> > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > 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? Regards, Yi L > } > > vtd_dev_as = vtd_bus->dev_as[devfn]; > -- > 2.7.4 > >
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 <jasowang@redhat.com> > > > > 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 <mst@redhat.com> > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: Richard Henderson <rth@twiddle.net> > > Cc: Eduardo Habkost <ehabkost@redhat.com> > > Acked-by: Peter Xu <peterx@redhat.com> > > Signed-off-by: Jason Wang <jasowang@redhat.com> > > Signed-off-by: Peter Xu <peterx@redhat.com> > > --- > > 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, -- peterx
> -----Original Message----- > From: Qemu-devel [mailto:qemu-devel-bounces+yi.l.liu=intel.com@nongnu.org] On > Behalf Of Peter Xu > Sent: Wednesday, December 14, 2016 11:06 AM > To: Liu, Yi L <yi.l.liu@linux.intel.com>; Jason Wang <jasowang@redhat.com> > Cc: Lan, Tianyu <tianyu.lan@intel.com>; Tian, Kevin <kevin.tian@intel.com>; > mst@redhat.com; jan.kiszka@siemens.com; bd.aviv@gmail.com; qemu- > devel@nongnu.org; alex.williamson@redhat.com; Liu, Yi <yi.liu@intel.com> > 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 <jasowang@redhat.com> > > > > > > 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 <mst@redhat.com> > > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > > Cc: Richard Henderson <rth@twiddle.net> > > > Cc: Eduardo Habkost <ehabkost@redhat.com> > > > Acked-by: Peter Xu <peterx@redhat.com> > > > Signed-off-by: Jason Wang <jasowang@redhat.com> > > > Signed-off-by: Peter Xu <peterx@redhat.com> > > > --- > > > 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
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); } vtd_dev_as = vtd_bus->dev_as[devfn];