[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2 01/13] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Sean Christopherson <seanjc@xxxxxxxxxx>
- Date: Thu, 16 Sep 2021 21:41:01 +0000
- Cc: Ingo Molnar <mingo@xxxxxxxxxx>, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Mark Rutland <mark.rutland@xxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Marc Zyngier <maz@xxxxxxxxxx>, Guo Ren <guoren@xxxxxxxxxx>, Nick Hu <nickhu@xxxxxxxxxxxxx>, Greentime Hu <green.hu@xxxxxxxxx>, Vincent Chen <deanbo422@xxxxxxxxx>, Paul Walmsley <paul.walmsley@xxxxxxxxxx>, Palmer Dabbelt <palmer@xxxxxxxxxxx>, Albert Ou <aou@xxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, x86@xxxxxxxxxx, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>, Jiri Olsa <jolsa@xxxxxxxxxx>, Namhyung Kim <namhyung@xxxxxxxxxx>, James Morse <james.morse@xxxxxxx>, Alexandru Elisei <alexandru.elisei@xxxxxxx>, Suzuki K Poulose <suzuki.poulose@xxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Wanpeng Li <wanpengli@xxxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, linux-perf-users@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, kvmarm@xxxxxxxxxxxxxxxxxxxxx, linux-csky@xxxxxxxxxxxxxxx, linux-riscv@xxxxxxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Artem Kashkanov <artem.kashkanov@xxxxxxxxx>, Like Xu <like.xu.linux@xxxxxxxxx>, Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
- Delivery-date: Thu, 16 Sep 2021 21:41:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Sat, Aug 28, 2021, Peter Zijlstra wrote:
> On Fri, Aug 27, 2021 at 05:35:46PM -0700, Sean Christopherson wrote:
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 464917096e73..2126f6327321 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -6491,14 +6491,19 @@ struct perf_guest_info_callbacks *perf_guest_cbs;
> >
> > int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks
> > *cbs)
> > {
> > - perf_guest_cbs = cbs;
> > + if (WARN_ON_ONCE(perf_guest_cbs))
> > + return -EBUSY;
> > +
> > + WRITE_ONCE(perf_guest_cbs, cbs);
> > + synchronize_rcu();
>
> You're waiting for all NULL users to go away? :-) IOW, we can do without
> this synchronize_rcu() call.
Doh, right. I was thinking KVM needed to wait for in-progress NMI to exit to
ensure guest PT interrupts are handled correctly, but obviously the NMI handler
needs to exit for that CPU to get into a guest...
> > return 0;
> > }
> > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
> >
> > int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks
> > *cbs)
> > {
> > - perf_guest_cbs = NULL;
>
> if (WARN_ON_ONCE(perf_guest_cbs != cbs))
> return -EBUSY;
>
> ?
Works for me. I guess I'm more optimistic about people not being morons :-)
|