Messages in this thread | | | Date | Fri, 10 Mar 2023 13:07:27 -0800 | Subject | Re: [RFC][PATCH 5/5] x86/kvm: Simplify static call handling | From | Sean Christopherson <> |
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"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.
It's not strictly necessary, but I'm inclinded to keep KVM_X86_OP_OPTIONAL_RET0 around for documentation purposes. And if I could figure out the compiler magic to make it work, a WARN/BUILD_BUG on the sizeof() the return type of a RET0 function being larger than sizeof(int). KVM encountered the fun that occurs on a u64 return on 32-bit kernels due to "xor eax, eax" leaving garbage in edx.
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