Messages in this thread | | | Date | Tue, 22 Jun 2010 11:04:48 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH V2 3/5] ara virt interface of perf to support kvm guest os statistics collection in guest os |
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On 06/22/2010 08:47 AM, Zhang, Yanmin wrote: > On Mon, 2010-06-21 at 16:56 +0300, Gleb Natapov wrote: > >> On Mon, Jun 21, 2010 at 05:31:43PM +0800, Zhang, Yanmin wrote: >> >>> The 3rd patch is to implement para virt perf at host kernel. >>> >>> Signed-off-by: Zhang Yanmin<yanmin_zhang@linux.intel.com> >>> >>> > <snip> > > >>> + >>> +static void kvm_copy_event_to_guest(struct kvm_vcpu *vcpu, >>> + struct perf_event *host_event) >>> +{ >>> + struct host_perf_shadow *shadow = host_event->host_perf_shadow; >>> + struct guest_perf_event counter; >>> + int ret; >>> + s32 overflows; >>> + >>> + ret = kvm_read_guest(vcpu->kvm, shadow->guest_event_addr, >>> + &counter, sizeof(counter)); >>> + if (ret< 0) >>> + return; >>> + >>> +again: >>> + overflows = atomic_read(&shadow->counter.overflows); >>> + if (atomic_cmpxchg(&shadow->counter.overflows, overflows, 0) != >>> + overflows) >>> + goto again; >>> + >>> + counter.count = shadow->counter.count; >>> + atomic_add(overflows,&counter.overflows); >>> + >>> + kvm_write_guest(vcpu->kvm, >>> + shadow->guest_event_addr, >>> + &counter, >>> + sizeof(counter)); >>> >> Those kind of interfaces worry me since the can cause bugs that are >> very hard to catch. What if guest enables some events and crashes into >> kdump kernel (or kexec new kernel) without reseting HW. Now host may >> write over guest memory without guest expecting it. Do you handle this >> scenario in a guest side? I think you need to register reboot notify >> and disable events from there. >> > Sorry for missing your comments. > > My patch could take care of dead guest os by cleaning up all events in function > kvm_arch_destroy_vm, so all events are closed if host user kills the guest > qemu process. > >
A reset does not involve destroying a vm; you have to clean up as part of the rest process.
Note MSRs are automatically cleared, so that's something in favour of an MSR interface.
> As for your scenario, I will register reboot notify and add a new pv perf > hypercall interface to vmexit to host kernel to do cleanup. >
You aren't guaranteed a reboot notifier will be called. On the other hand, we need a kexec handler.
-- error compiling committee.c: too many arguments to function
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