linux-kernel - [PATCH v2 26/32] KVM: nVMX: Selectively use TLB_FLUSH

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Message-Id: <20200317045238.30434-27-sean.j.christopherson@intel.com>
Date:   Mon, 16 Mar 2020 21:52:32 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...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, Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH v2 26/32] KVM: nVMX: Selectively use TLB_FLUSH_CURRENT for nested VM-Enter/VM-Exit

Flush only the current context, as opposed to all contexts, when
requesting a TLB flush to handle the scenario where a L1 does not expect
a TLB flush, but one is required because L1 and L2 shared an ASID.  This
occurs if EPT is disabled (no per-EPTP tag), VPID is enabled (hardware
doesn't flush unconditionally) and vmcs02 does not have its own VPID due
to exhaustion of available VPIDs.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/nested.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 19600d4b3344..04cdf7ded1d3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1167,16 +1167,19 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
 	 *
 	 * If VPID is enabled and used by vmc12, but L2 does not have a unique
 	 * TLB tag (ASID), i.e. EPT is disabled and KVM was unable to allocate
-	 * a VPID for L2, flush the TLB as the effective ASID is common to both
-	 * L1 and L2.
+	 * a VPID for L2, flush the current context as the effective ASID is
+	 * common to both L1 and L2.
 	 *
 	 * Defer the flush so that it runs after vmcs02.EPTP has been set by
 	 * KVM_REQ_LOAD_MMU_PGD (if nested EPT is enabled) and to avoid
 	 * redundant flushes further down the nested pipeline.
 	 */
-	if (enable_vpid &&
-	    (!nested_cpu_has_vpid(vmcs12) || !nested_has_guest_tlb_tag(vcpu)))
-		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+	if (enable_vpid) {
+		if (!nested_cpu_has_vpid(vmcs12))
+			kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+		else if (!nested_has_guest_tlb_tag(vcpu))
+			kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
+	}
 }
 
 static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)
-- 
2.24.1