linux-kernel - [PATCH v13 07/48] KVM: x86: Move clearing of TLB_FLUSH_CURRENT to kvm_vcpu_flush_tlb

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Date:   Tue,  1 Nov 2022 15:53:45 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v13 07/48] KVM: x86: Move clearing of TLB_FLUSH_CURRENT to kvm_vcpu_flush_tlb_all()

From: Sean Christopherson <seanjc@...gle.com>

Clear KVM_REQ_TLB_FLUSH_CURRENT in kvm_vcpu_flush_tlb_all() instead of in
its sole caller that processes KVM_REQ_TLB_FLUSH.  Regardless of why/when
kvm_vcpu_flush_tlb_all() is called, flushing "all" TLB entries also
flushes "current" TLB entries.

Ideally, there will never be another caller of kvm_vcpu_flush_tlb_all(),
and moving the handling "requires" extra work to document the ordering
requirement, but future Hyper-V paravirt TLB flushing support will add
similar logic for flush "guest" (Hyper-V can flush a subset of "guest"
entries).  And in the Hyper-V case, KVM needs to do more than just clear
the request, the queue of GPAs to flush also needs to purged, and doing
all only in the request path is undesirable as kvm_vcpu_flush_tlb_guest()
does have multiple callers (though it's unlikely KVM's paravirt TLB flush
will coincide with Hyper-V's paravirt TLB flush).

Move the logic even though it adds extra "work" so that KVM will be
consistent with how flush requests are processed when the Hyper-V support
lands.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/x86.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f618187585b1..fdda5f447f87 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3396,6 +3396,9 @@ static void kvm_vcpu_flush_tlb_all(struct kvm_vcpu *vcpu)
 {
 	++vcpu->stat.tlb_flush;
 	static_call(kvm_x86_flush_tlb_all)(vcpu);
+
+	/* Flushing all ASIDs flushes the current ASID... */
+	kvm_clear_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
 }

 static void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu)
@@ -10477,12 +10480,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			kvm_mmu_sync_roots(vcpu);
 		if (kvm_check_request(KVM_REQ_LOAD_MMU_PGD, vcpu))
 			kvm_mmu_load_pgd(vcpu);
-		if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {
+
+		/*
+		 * Note, the order matters here, as flushing "all" TLB entries
+		 * also flushes the "current" TLB entries, i.e. servicing the
+		 * flush "all" will clear any request to flush "current".
+		 */
+		if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu))
 			kvm_vcpu_flush_tlb_all(vcpu);

-			/* Flushing all ASIDs flushes the current ASID... */
-			kvm_clear_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
-		}
 		kvm_service_local_tlb_flush_requests(vcpu);

 		if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
-- 
2.37.3