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 18:28:07 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     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()

On 21/02/20 16:32, Sean Christopherson wrote:
>> 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?
> Ah rats.  I lost track of that functional change between making the commit
> and writing the changelog.
> 
> I'll spin a v2 to rewrite the changelog, and maybe add the "vpid == 0"
> check in a separate patch.
> 

What about this:

diff --git a/arch/x86/kvm/vmx/ops.h b/arch/x86/kvm/vmx/ops.h
index eb6adc77a55d..2ab88984b22f 100644
--- a/arch/x86/kvm/vmx/ops.h
+++ b/arch/x86/kvm/vmx/ops.h
@@ -255,13 +255,10 @@ static inline void __invept(unsigned long ext, u64 eptp, gpa_t gpa)
 
 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);
-	else
+	if (!cpu_has_vmx_invvpid_single())
 		__invvpid(VMX_VPID_EXTENT_ALL_CONTEXT, 0, 0);
+	else if (vpid != 0)
+		__invvpid(VMX_VPID_EXTENT_SINGLE_CONTEXT, vpid, 0);
 }
 
 static inline void vpid_sync_vcpu_addr(int vpid, gva_t addr)