linux-kernel - Re: [PATCH v2 04/11] KVM: SEV: publish supported VMSA features

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Message-ID: <43b9125f-35d4-4368-8783-a41799b11c21@redhat.com>
Date: Fri, 23 Feb 2024 17:41:58 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, michael.roth@....com,
 aik@....com
Subject: Re: [PATCH v2 04/11] KVM: SEV: publish supported VMSA features

On 2/23/24 17:07, Sean Christopherson wrote:
>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>> index f760106c31f8..53e958805ab9 100644
>> --- a/arch/x86/kvm/svm/sev.c
>> +++ b/arch/x86/kvm/svm/sev.c
>> @@ -59,10 +59,12 @@ module_param_named(sev_es, sev_es_enabled, bool, 0444);
>>   /* enable/disable SEV-ES DebugSwap support */
>>   static bool sev_es_debug_swap_enabled = true;
>>   module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
>> +static u64 sev_supported_vmsa_features;
>>   #else
>>   #define sev_enabled false
>>   #define sev_es_enabled false
>>   #define sev_es_debug_swap_enabled false
>> +#define sev_supported_vmsa_features 0
> 
> Ok, I've reached my breaking point.  Compiling sev.c for CONFIG_KVM_AMD_SEV=n is
> getting untenable.  Splattering #ifdefs _inside_ SEV specific functions is weird
> and confusing.

Ok, I think in some cases I prefer stubs but I'll weave your 4 patches 
in v3.

Paolo

> And unless dead code elimination isn't as effective as I think it is, we don't
> even need any stuba  since sev_guest() and sev_es_guest() are __always_inline
> specifically so that useless code can be elided.  Or if we want to avoid use of
> IS_ENABLED(), we could add four stubs, which is still well worth it.
> 
> Note, I also have a separate series that I will post today (I hope) that gives
> __svm_sev_es_vcpu_run() similar treatment (the 32-bit "support" in assembly is
> all kinds of stupid).
> 
> Attached patches are compile-tested only, though I'll try to take them for a spin
> on hardware later today.