On Mon, 9 Dec 2019 20:12:09 +1100 Gavin Shan <gs...@redhat.com> wrote:
> On 12/9/19 7:36 PM, Greg Kurz wrote: > > On Sun, 8 Dec 2019 00:14:00 +1100 > > Gavin Shan <gs...@redhat.com> wrote: > > > >> On 12/7/19 3:50 AM, Greg Kurz wrote: > >>> On Fri, 6 Dec 2019 17:36:42 +1100 > >>> Gavin Shan <gs...@redhat.com> wrote: > >>> > >>>> object_dynamic_cast() should return machine (or GPIO) state instad of NMI > >>>> state in do_nmi(). So it's wrong to convert it to NMI state > >>>> unconditionally. > >>>> > >>> > >>> object_dynamic_cast() returns either its first argument if it can be cast > >>> to the given typename or NULL. Since the x86, ccw and spapr machines and > >>> the PowerMac GPIO implement the NMI interface, nothing is wrong here. > >>> > >>> The do_nmi() function is called for all objects in the QOM tree and simply > >>> filters out the ones that don't implement the NMI interface. > >>> > >>> I do agree that this isn't super obvious though. It would be clearer to > >>> do the filtering in the foreach() function. Something like: > >>> > >>> https://patchwork.ozlabs.org/patch/1182232/ > >>> > >> > >> Greg, Thanks for the review and comments. I think we're talking about > >> different issues. I do agree it's worthy to simplify the code with the > >> object_child_foreach_type(), but later. > >> > >> When we have below parameters to qemu, object_dynamic_cast(o, TYPE_NMI) > >> returns object of "pc-q35-4.2-machine", which is passed to the subquent > >> NMIClass::nmi_monitor_handler(). However, the function expects a NMIState > >> from its prototype as below. This patch changes the prototype to fill the > >> gap. > >> > >> void (*nmi_monitor_handler)(NMIState *n, int cpu_index, Error **errp); > >> > > > > Hmm... the "pc-q35-4.2-machine" type inherits from the TYPE_PC_MACHINE, > > which in turns inherits from TYPE_X86_MACHINE, which implements the > > TYPE_NMI interface. It thus seems okay to pass this object to x86_nmi(). > > > > What are you trying to fix here ? > > > > There is no valid instance associated with interface class. For this specific > case, there is no NMIState instance. I don't understand how we can pass a > valid NMIState to the function. Ah I get it. Please read the include/qom/object.h to understand what QOM interfaces are about. Especially this paragraph: * # Interfaces # * * Interfaces allow a limited form of multiple inheritance. Instances are * similar to normal types except for the fact that are only defined by * their classes and never carry any state. You can dynamically cast an object * to one of its #Interface types and vice versa. > Furthermore, below code returns "pc-q35-4.2-machine" > object instead of NMIState. It's not safe to do the forced conversion here. > > /* It returns "pc-q35-4.2-machine" instance */ > NMIState *n = (NMIState *) object_dynamic_cast(o, TYPE_NMI); > : > nc->nmi_monitor_handler(n, ns->cpu_index, &ns->err); As explained in my previous mail, this _forced conversion_ is the current way to implement object_child_foreach_type(). It is ugly and confusing for newcomers but it is safe since the pointer is either TYPE_NMI or NULL, in which case the handler isn't called. > > > If "struct NMIState" is declared and the data struct is written in the > function. > We will run into data corruption if I'm correct. > The 'struct NMIState' isn't defined on purpose, but I agree this isn't documented anywhere except in this changelog: commit 00ed3da9b5c2e66e796a172df3e19545462b9c90 Author: David Gibson <da...@gibson.dropbear.id.au> Date: Tue Sep 24 16:00:33 2019 +1000 xics: Minor fixes for XICSFabric interface Interface instances should never be directly dereferenced. So, the common practice is to make them incomplete types to make sure no-one does that. XICSFrabric, however, had a dummy type which is less safe. We were also using OBJECT_CHECK() where we should have been using INTERFACE_CHECK(). Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> Reviewed-by: Greg Kurz <gr...@kaod.org> Reviewed-by: Cédric Le Goater <c...@kaod.org> Maybe the NMIState naming was a poor choice since there's no associated state with QOM interfaces. But we do want to keep a typedef though: it is more precise and hence safer to pass an NMIState * than an Object *. > I'm pasting the message I had. Hope this helps for understanding the issue: > > --- a/hw/core/nmi.c > +++ b/hw/core/nmi.c > @@ -42,6 +42,10 @@ static int do_nmi(Object *o, void *opaque) > if (n) { > NMIClass *nc = NMI_GET_CLASS(n); > > + fprintf(stdout, "%s: o=%s, n=%s\n", > + __func__, object_get_typename(OBJECT(o)), > + object_get_typename(OBJECT(n))); > + > object_get_typename() returns the type of the instance, which is either a machine or a GPIO in the current code base. This is different from object_dynamic_cast() which just tells if a given object can be cast to a give type (either regular QOM type or QOM interface). It is up to the various NMIClass::nmi_monitor_handler() to make sure they're being passed the right object. macio_gpio_nmi() explicitly does that with MACIO_GPIO(n). The other ones only need to access the CPU state and end up checking it is valid: s390_nmi() checks S390_CPU(cs), x86_nmi() checks X86_CPU(cs) and spapr_nmi() ->async_run_on_cpu() ->spapr_do_system_reset_on_cpu() ->ppc_cpu_do_system_reset() checks POWERPC_CPU(cs) but they could maybe assert(object_dynamic_cast()) as well for clarity. > > # QEMU 4.1.93 monitor - type 'help' for more information > (qemu) nmi > do_nmi: o=pc-q35-4.2-machine, n=pc-q35-4.2-machine > > > >> Changed to: > >> > >> void (*nmi_monitor_handler)(Object *parent, int cpu_index, Error > >> **errp); > >> > >> ~/sandbox/src/qemu/qemu.main.x86/x86_64-softmmu/qemu-system-x86_64 > >> \ > >> --enable-kvm -machine type=q35,accel=kvm,kernel-irqchip=on -cpu host > >> -smp 2 -m 1G \ > >> -monitor none -serial mon:stdio -nographic -s > >> \ > >> -bios ~/sandbox/src/firmware/seabios/out/bios.bin > >> \ > >> -kernel ~/sandbox/src/linux/linux.main.x86/arch/x86/boot/bzImage > >> \ > >> -initrd ~/sandbox/src/util/buildroot/output/images/rootfs.cpio.xz > >> \ > >> -append "earlyprintk=ttyS0 console=ttyS0 debug" > >> \ > >> -device virtio-net-pci,netdev=unet,mac=52:54:00:f1:26:a6 > >> \ > >> -netdev user,id=unet,hostfwd=tcp::50959-:22 > >> \ > >> -drive file=~/sandbox/images/vm.img,if=none,format=raw,id=nvme0 > >> \ > >> -device nvme,drive=nvme0,serial=foo > >> \ > >> -drive file=~/sandbox/images/vm1.img,if=none,format=raw,id=nvme1 > >> \ > >> -device nvme,drive=nvme1,serial=foo1 > >> > >>>> This changes the prototype of NMIClass::nmi_monitor_handler() to accept > >>>> the parent object of NMI state instead of itself. With this, he parent > >>>> object > >>>> is passed to the function, to avoid potential data corruption. > >>>> > >>>> Signed-off-by: Gavin Shan <gs...@redhat.com> > >>>> --- > >>>> hw/core/nmi.c | 8 ++++---- > >>>> hw/i386/x86.c | 2 +- > >>>> hw/misc/macio/gpio.c | 6 +++--- > >>>> hw/ppc/spapr.c | 2 +- > >>>> hw/s390x/s390-virtio-ccw.c | 2 +- > >>>> include/hw/nmi.h | 2 +- > >>>> 6 files changed, 11 insertions(+), 11 deletions(-) > >>>> > >>>> diff --git a/hw/core/nmi.c b/hw/core/nmi.c > >>>> index 481c4b3c7e..554708d0db 100644 > >>>> --- a/hw/core/nmi.c > >>>> +++ b/hw/core/nmi.c > >>>> @@ -37,13 +37,13 @@ static void nmi_children(Object *o, struct do_nmi_s > >>>> *ns); > >>>> static int do_nmi(Object *o, void *opaque) > >>>> { > >>>> struct do_nmi_s *ns = opaque; > >>>> - NMIState *n = (NMIState *) object_dynamic_cast(o, TYPE_NMI); > >>>> + Object *parent = object_dynamic_cast(o, TYPE_NMI); > >>>> > >>>> - if (n) { > >>>> - NMIClass *nc = NMI_GET_CLASS(n); > >>>> + if (parent) { > >>>> + NMIClass *nc = NMI_GET_CLASS(parent); > >>>> > >>>> ns->handled = true; > >>>> - nc->nmi_monitor_handler(n, ns->cpu_index, &ns->err); > >>>> + nc->nmi_monitor_handler(parent, ns->cpu_index, &ns->err); > >>>> if (ns->err) { > >>>> return -1; > >>>> } > >>>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c > >>>> index 394edc2f72..b98204f104 100644 > >>>> --- a/hw/i386/x86.c > >>>> +++ b/hw/i386/x86.c > >>>> @@ -190,7 +190,7 @@ const CPUArchIdList > >>>> *x86_possible_cpu_arch_ids(MachineState *ms) > >>>> return ms->possible_cpus; > >>>> } > >>>> > >>>> -static void x86_nmi(NMIState *n, int cpu_index, Error **errp) > >>>> +static void x86_nmi(Object *parent, int cpu_index, Error **errp) > >>>> { > >>>> /* cpu index isn't used */ > >>>> CPUState *cs; > >>>> diff --git a/hw/misc/macio/gpio.c b/hw/misc/macio/gpio.c > >>>> index 6cca6b27d6..6b4dfcc188 100644 > >>>> --- a/hw/misc/macio/gpio.c > >>>> +++ b/hw/misc/macio/gpio.c > >>>> @@ -196,10 +196,10 @@ static void macio_gpio_reset(DeviceState *dev) > >>>> macio_set_gpio(s, 1, true); > >>>> } > >>>> > >>>> -static void macio_gpio_nmi(NMIState *n, int cpu_index, Error **errp) > >>>> +static void macio_gpio_nmi(Object *parent, int cpu_index, Error **errp) > >>>> { > >>>> - macio_set_gpio(MACIO_GPIO(n), 9, true); > >>>> - macio_set_gpio(MACIO_GPIO(n), 9, false); > >>>> + macio_set_gpio(MACIO_GPIO(parent), 9, true); > >>>> + macio_set_gpio(MACIO_GPIO(parent), 9, false); > >>>> } > >>>> > >>>> static void macio_gpio_class_init(ObjectClass *oc, void *data) > >>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > >>>> index e076f6023c..3b92e4013d 100644 > >>>> --- a/hw/ppc/spapr.c > >>>> +++ b/hw/ppc/spapr.c > >>>> @@ -3377,7 +3377,7 @@ void spapr_do_system_reset_on_cpu(CPUState *cs, > >>>> run_on_cpu_data arg) > >>>> ppc_cpu_do_system_reset(cs); > >>>> } > >>>> > >>>> -static void spapr_nmi(NMIState *n, int cpu_index, Error **errp) > >>>> +static void spapr_nmi(Object *parent, int cpu_index, Error **errp) > >>>> { > >>>> CPUState *cs; > >>>> > >>>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c > >>>> index d3edeef0ad..a49952a8b9 100644 > >>>> --- a/hw/s390x/s390-virtio-ccw.c > >>>> +++ b/hw/s390x/s390-virtio-ccw.c > >>>> @@ -431,7 +431,7 @@ static void s390_hot_add_cpu(MachineState *machine, > >>>> s390x_new_cpu(object_class_get_name(oc), id, errp); > >>>> } > >>>> > >>>> -static void s390_nmi(NMIState *n, int cpu_index, Error **errp) > >>>> +static void s390_nmi(Object *parent, int cpu_index, Error **errp) > >>>> { > >>>> CPUState *cs = qemu_get_cpu(cpu_index); > >>>> > >>>> diff --git a/include/hw/nmi.h b/include/hw/nmi.h > >>>> index a1e128724e..75afa67790 100644 > >>>> --- a/include/hw/nmi.h > >>>> +++ b/include/hw/nmi.h > >>>> @@ -38,7 +38,7 @@ typedef struct NMIState NMIState; > >>>> typedef struct NMIClass { > >>>> InterfaceClass parent_class; > >>>> > >>>> - void (*nmi_monitor_handler)(NMIState *n, int cpu_index, Error > >>>> **errp); > >>>> + void (*nmi_monitor_handler)(Object *parent, int cpu_index, Error > >>>> **errp); > >>>> } NMIClass; > >>>> > >>>> void nmi_monitor_handle(int cpu_index, Error **errp); > >>> > > Regards, > Gavin >
