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Re: [PATCH 00/15] perf: KVM: Fix, optimize, and clean up callbacks
- To: Like Xu <like.xu.linux@xxxxxxxxx>
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Fri, 27 Aug 2021 09:44:52 +0200
- Cc: Sean Christopherson <seanjc@xxxxxxxxxx>, 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>, Zhu Lingshan <lingshan.zhu@xxxxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Mark Rutland <mark.rutland@xxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>, 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>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Jason Baron <jbaron@xxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Ard Biesheuvel <ardb@xxxxxxxxxx>
- Delivery-date: Fri, 27 Aug 2021 07:48:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, Aug 27, 2021 at 02:52:25PM +0800, Like Xu wrote:
> + STATIC BRANCH/CALL friends.
>
> On 27/8/2021 8:57 am, Sean Christopherson wrote:
> > This started out as a small series[1] to fix a KVM bug related to Intel PT
> > interrupt handling and snowballed horribly.
> >
> > The main problem being addressed is that the perf_guest_cbs are shared by
> > all CPUs, can be nullified by KVM during module unload, and are not
> > protected against concurrent access from NMI context.
>
> Shouldn't this be a generic issue of the static_call() usage ?
>
> At the beginning, we set up the static entry assuming perf_guest_cbs != NULL:
>
> if (perf_guest_cbs && perf_guest_cbs->handle_intel_pt_intr) {
> static_call_update(x86_guest_handle_intel_pt_intr,
> perf_guest_cbs->handle_intel_pt_intr);
> }
>
> and then we unset the perf_guest_cbs and do the static function call like
> this:
>
> DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr,
> *(perf_guest_cbs->handle_intel_pt_intr));
> static int handle_pmi_common(struct pt_regs *regs, u64 status)
> {
> ...
> if (!static_call(x86_guest_handle_intel_pt_intr)())
> intel_pt_interrupt();
> ...
> }
You just have to make sure all static_call() invocations that started
before unreg are finished before continuing with the unload.
synchronize_rcu() can help with that.
This is module unload 101. Nothing specific to static_call().
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