linux-kernel - Re: [PATCH v2 24/49] KVM: x86: #undef SPEC_CTRL_SSBD in cpuid.c to avoid macro collisions

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Message-ID: <20d3017a8dd54b345104bf2e5cb888a22a1e0a53.camel@redhat.com>
Date: Thu, 04 Jul 2024 21:30:43 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Hou Wenlong
 <houwenlong.hwl@...group.com>, Kechen Lu <kechenl@...dia.com>, Oliver Upton
 <oliver.upton@...ux.dev>, Binbin Wu <binbin.wu@...ux.intel.com>, Yang
 Weijiang <weijiang.yang@...el.com>, Robert Hoo <robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 24/49] KVM: x86: #undef SPEC_CTRL_SSBD in cpuid.c to
 avoid macro collisions

On Fri, 2024-05-17 at 10:39 -0700, Sean Christopherson wrote:
> Undefine SPEC_CTRL_SSBD, which is #defined by msr-index.h to represent the
> enable flag in MSR_IA32_SPEC_CTRL, to avoid issues with the macro being
> unpacked into its raw value when passed to KVM's F() macro.  This will
> allow using multiple layers of macros in F() and friends, e.g. to harden
> against incorrect usage of F().
> 
> No functional change intended (cpuid.c doesn't consume SPEC_CTRL_SSBD).
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/cpuid.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8efffd48cdf1..a16d6e070c11 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -639,6 +639,12 @@ static __always_inline void kvm_cpu_cap_init(u32 leaf, u32 mask)
>  	kvm_cpu_caps[leaf] &= raw_cpuid_get(cpuid);
>  }
>  
> +/*
> + * Undefine the MSR bit macro to avoid token concatenation issues when
> + * processing X86_FEATURE_SPEC_CTRL_SSBD.
> + */
> +#undef SPEC_CTRL_SSBD
> +
>  void kvm_set_cpu_caps(void)
>  {
>  	memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps));

Hi,

Maybe we should instead rename the 
SPEC_CTRL_SSBD to 'MSR_IA32_SPEC_CTRL_SSBD' and together with it, other fields of this msr.
It seems that at least some msrs in this file do this.

Best regards,
	Maxim Levitsky