Re: [PATCH v3 6/6] KVM: x86: allow defining return-0 static calls

Paolo Bonzini
2022-02-18T17:20:30Z

On 2/18/22 17:29, Sean Christopherson wrote:
> On Thu, Feb 17, 2022, Paolo Bonzini wrote:
>> A few vendor callbacks are only used by VMX, but they return an integer
>> or bool value. Introduce KVM_X86_OP_OPTIONAL_RET0 for them: if a func is
>> NULL in struct kvm_x86_ops, it will be changed to __static_call_return0
>> when updating static calls.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> arch/x86/include/asm/kvm-x86-ops.h | 15 +++++++++------
>> arch/x86/include/asm/kvm_host.h | 4 ++++
>> arch/x86/kvm/svm/avic.c | 5 -----
>> arch/x86/kvm/svm/svm.c | 20 --------------------
>> arch/x86/kvm/x86.c | 2 +-
>> kernel/static_call.c | 1 +
>> 6 files changed, 15 insertions(+), 32 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
>> index c0ec066a8599..29affccb353c 100644
>> --- a/arch/x86/include/asm/kvm-x86-ops.h
>> +++ b/arch/x86/include/asm/kvm-x86-ops.h
>> @@ -10,7 +10,9 @@ BUILD_BUG_ON(1)
>> *
>> * KVM_X86_OP_OPTIONAL() can be used for those functions that can have
>> * a NULL definition, for example if "static_call_cond()" will be used
>> - * at the call sites.
>> + * at the call sites. KVM_X86_OP_OPTIONAL_RET0() can be used likewise
>> + * to make a definition optional, but in this case the default will
>> + * be __static_call_return0.
>
> __static_call_return0()
>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index ab1c4778824a..d3da64106685 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -131,6 +131,7 @@ struct kvm_x86_ops kvm_x86_ops __read_mostly;
>> DEFINE_STATIC_CALL_NULL(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>
>> EXPORT_STATIC_CALL_GPL(kvm_x86_get_cs_db_l_bits);
>> EXPORT_STATIC_CALL_GPL(kvm_x86_cache_reg);
>> @@ -12016,7 +12017,6 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>> static inline bool kvm_guest_apic_has_interrupt(struct kvm_vcpu *vcpu)
>> {
>> return (is_guest_mode(vcpu) &&
>> - kvm_x86_ops.guest_apic_has_interrupt &&
>> static_call(kvm_x86_guest_apic_has_interrupt)(vcpu));
>
> Can you opportunistically align the indentation and drop the outer parantheses? I.e.
>
> return is_guest_mode(vcpu) &&
> static_call(kvm_x86_guest_apic_has_interrupt)(vcpu);

Hmm, I like having the parentheses (despite "return not being a
function") because editors are inconsistent in what indentation to use
after return.

Some use a tab (which does the right thing just by chance with Linux
because "return " is as long as a tab is wide), but vim for example does
the totally awkward

int f()
{
return a &&
b;
}

Of course I can fix the indentation.

Paolo

>> }
>>
>> diff --git a/kernel/static_call.c b/kernel/static_call.c
>> index 43ba0b1e0edb..76abd46fe6ee 100644
>> --- a/kernel/static_call.c
>> +++ b/kernel/static_call.c
>> @@ -503,6 +503,7 @@ long __static_call_return0(void)
>> {
>> return 0;
>> }
>> +EXPORT_SYMBOL_GPL(__static_call_return0)
>
> This doesn't compile, it needs a semicolon.
>