Messages in this thread | | | Date | Fri, 10 Mar 2023 21:29:36 +0000 | Subject | Re: [RFC][PATCH 5/5] x86/kvm: Simplify static call handling | From | Sean Christopherson <> |
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On Fri, Mar 10, 2023, Steven Rostedt wrote: > On Fri, 10 Mar 2023 13:07:27 -0800 > Sean Christopherson <seanjc@google.com> wrote: > > > "KVM: x86:" please, "x86/kvm" is for guest-side changes. > > > > On Fri, Mar 10, 2023, Josh Poimboeuf wrote: > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > > index 1dfba499d3e5..612531e1c478 100644 > > > --- a/arch/x86/include/asm/kvm_host.h > > > +++ b/arch/x86/include/asm/kvm_host.h > > > @@ -1789,8 +1789,6 @@ extern struct kvm_x86_ops kvm_x86_ops; > > > > > > #define KVM_X86_OP(func) \ > > > DECLARE_STATIC_CALL(kvm_x86_##func, *(((struct kvm_x86_ops *)0)->func)); > > > -#define KVM_X86_OP_OPTIONAL KVM_X86_OP > > > -#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP > > > #include <asm/kvm-x86-ops.h> > > > > > > int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops); > > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > > > index 6accb46295a3..5f7f860c5f17 100644 > > > --- a/arch/x86/kvm/pmu.c > > > +++ b/arch/x86/kvm/pmu.c > > > @@ -77,20 +77,15 @@ static struct kvm_pmu_ops kvm_pmu_ops __read_mostly; > > > #define KVM_X86_PMU_OP(func) \ > > > DEFINE_STATIC_CALL_NULL(kvm_x86_pmu_##func, \ > > > *(((struct kvm_pmu_ops *)0)->func)); > > > -#define KVM_X86_PMU_OP_OPTIONAL KVM_X86_PMU_OP > > > #include <asm/kvm-x86-pmu-ops.h> > > > > > > void kvm_pmu_ops_update(const struct kvm_pmu_ops *pmu_ops) > > > { > > > memcpy(&kvm_pmu_ops, pmu_ops, sizeof(kvm_pmu_ops)); > > > > > > -#define __KVM_X86_PMU_OP(func) \ > > > - static_call_update(kvm_x86_pmu_##func, kvm_pmu_ops.func); > > > #define KVM_X86_PMU_OP(func) \ > > > - WARN_ON(!kvm_pmu_ops.func); __KVM_X86_PMU_OP(func) > > > > I would much prefer to keep KVM mostly as-is, specifically so that we don't lose > > this WARN_ON() that guards against a vendor module neglecting to implement a > > mandatory callback. This effectively gives KVM "full" protection against consuming > > an unexpectedly-NULL function pointer. > > As in my reply to patch 0/5, I suggested that static_call_update(NULL) > would trigger a WARN_ON() always. Then this could be cleaned up and still > get that warning.
I don't think that provides the functionality KVM wants/needs. KVM only disallows NULL updates for select mandatory hooks. For optional hooks, KVM needs to support NULL updates in some capacity to handle the scenario where a vendor module is reloaded with different settings, e.g. loading kvm_intel with enable_apicv=0 after running with enable_apicv=1.
WARN_ON() a static_call_update(..., NULL) should be ok, but I believe KVM would still need/want macro shenanigans, e.g.
#define __KVM_X86_OP(func) \ static_call_update(kvm_x86_##func, kvm_x86_ops.func ? kvm_x86_ops.func : STATIC_CALL_NOP); #define KVM_X86_OP(func) \ WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func) #define KVM_X86_OP_OPTIONAL __KVM_X86_OP #define KVM_X86_OP_OPTIONAL_RET0(func) __KVM_X86_OP
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