linux-kernel - Re: [PATCH 04/10] KVM: VMX: Fold vpid_sync_vcpu_{single,global}() into vpid_sync

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Date:   Fri, 21 Feb 2020 14:39:51 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/10] KVM: VMX: Fold vpid_sync_vcpu_{single,global}() into vpid_sync_context()

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Fold vpid_sync_vcpu_global() and vpid_sync_vcpu_single() into their sole
> caller.  KVM should always prefer the single variant, i.e. the only
> reason to use the global variant is if the CPU doesn't support
> invalidating a single VPID, which is the entire purpose of wrapping the
> calls with vpid_sync_context().
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/ops.h | 16 ++--------------
>  1 file changed, 2 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/ops.h b/arch/x86/kvm/vmx/ops.h
> index 612df1bdb26b..eb6adc77a55d 100644
> --- a/arch/x86/kvm/vmx/ops.h
> +++ b/arch/x86/kvm/vmx/ops.h
> @@ -253,29 +253,17 @@ static inline void __invept(unsigned long ext, u64 eptp, gpa_t gpa)
>  	vmx_asm2(invept, "r"(ext), "m"(operand), ext, eptp, gpa);
>  }
>  
> -static inline void vpid_sync_vcpu_single(int vpid)
> +static inline void vpid_sync_context(int vpid)
>  {
>  	if (vpid == 0)
>  		return;
>  
>  	if (cpu_has_vmx_invvpid_single())
>  		__invvpid(VMX_VPID_EXTENT_SINGLE_CONTEXT, vpid, 0);
> -}
> -
> -static inline void vpid_sync_vcpu_global(void)
> -{
> -	if (cpu_has_vmx_invvpid_global())
> +	else
>  		__invvpid(VMX_VPID_EXTENT_ALL_CONTEXT, 0, 0);
>  }
>  
> -static inline void vpid_sync_context(int vpid)
> -{
> -	if (cpu_has_vmx_invvpid_single())
> -		vpid_sync_vcpu_single(vpid);
> -	else
> -		vpid_sync_vcpu_global();
> -}
> -
>  static inline void vpid_sync_vcpu_addr(int vpid, gva_t addr)
>  {
>  	if (vpid == 0)

In the original code it's only vpid_sync_vcpu_single() which has 'vpid
== 0' check, vpid_sync_vcpu_global() doesn't have it. So in the
hypothetical situation when cpu_has_vmx_invvpid_single() is false AND
we've e.g. exhausted our VPID space and allocate_vpid() returned zero,
the new code just won't do anything while the old one would've done
__invvpid(VMX_VPID_EXTENT_ALL_CONTEXT, 0, 0), right?

-- 
Vitaly