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Subject: Re: [PATCH v2 2/3] KVM: x86: introduce definitions to support static
 calls for kvm_x86_ops
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     seanjc@google.com, kvm@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andrea Arcangeli <aarcange@redhat.com>
References: <cover.1610680941.git.jbaron@akamai.com>
 <e5cc82ead7ab37b2dceb0837a514f3f8bea4f8d1.1610680941.git.jbaron@akamai.com>
 <YAFf2+nvhvWjGImy@hirez.programming.kicks-ass.net>
 <84b2f5ba-1a16-cb01-646c-37e25d659650@redhat.com>
From:   Jason Baron <jbaron@akamai.com>
Message-ID: <2e2cd2d9-e010-b435-3aba-35bac1b4cc14@akamai.com>
Date:   Fri, 15 Jan 2021 10:03:53 -0500
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On 1/15/21 8:50 AM, Paolo Bonzini wrote:
> On 15/01/21 10:26, Peter Zijlstra wrote:
>>> +#define KVM_X86_OP(func)                         \
>>> +    DEFINE_STATIC_CALL_NULL(kvm_x86_##func,                 \
>>> +                *(((struct kvm_x86_ops *)0)->func));
>>> +#define KVM_X86_OP_NULL 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);
>>> +EXPORT_STATIC_CALL_GPL(kvm_x86_tlb_flush_current);
>> Would something like:
>>
>>   
>> https://urldefense.com/v3/__https://lkml.kernel.org/r/20201110103909.GD2594@hirez.programming.kicks-ass.net__;!!GjvTz_vk!GbAPurpdyP1TaDRZN0NvvBkOLJhmRHzNtv0ZVIwZqNrJpMYze75mJzpUNJMRAg$
>>
>> Be useful? That way modules can call the static_call() but not change
>> it.
>>
> 
> Maybe not in these cases, but in general there may be cases where we later want to change the static_call (for example replacing jump labels with
> static_calls).
> 
> Paolo
> 

I tried this out but got:

ERROR: modpost: "__SCK__kvm_x86_cache_reg" [arch/x86/kvm/kvm-amd.ko] undefined!
ERROR: modpost: "__SCK__kvm_x86_tlb_flush_current" [arch/x86/kvm/kvm-intel.ko] undefined!
ERROR: modpost: "__SCK__kvm_x86_get_cs_db_l_bits" [arch/x86/kvm/kvm-intel.ko] undefined!
ERROR: modpost: "__SCK__kvm_x86_cache_reg" [arch/x86/kvm/kvm-intel.ko] undefined!

I'm a bit confused because we have:

#define __static_call(name)                                             \
({                                                                      \
        __ADDRESSABLE(STATIC_CALL_KEY(name));                           \
        &STATIC_CALL_TRAMP(name);                                       \
})

And so it looks to me like we need to still reference the key from the module code.

Thanks,

-Jason