linux-kernel - [PATCH V2 04/10] KVM: X86: Don't flush current tlb on shadow page modification

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Date:   Sat, 18 Sep 2021 08:56:30 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org
Subject: [PATCH V2 04/10] KVM: X86: Don't flush current tlb on shadow page modification

From: Lai Jiangshan <laijs@...ux.alibaba.com>

After any shadow page modification, flushing tlb only on current VCPU
is weird due to other VCPU's tlb might still be stale.

In other words, if there is any mandatory tlb-flushing after shadow page
modification, SET_SPTE_NEED_REMOTE_TLB_FLUSH or remote_flush should be
set and the tlbs of all VCPUs should be flushed.  There is not point to
only flush current tlb except when the request is from vCPU's or pCPU's
activities.

If there was any bug that mandatory tlb-flushing is required and
SET_SPTE_NEED_REMOTE_TLB_FLUSH/remote_flush is failed to set, this patch
would expose the bug in a more destructive way.  The related code paths
are checked and no missing SET_SPTE_NEED_REMOTE_TLB_FLUSH is found yet.

Currently, there is no optional tlb-flushing after sync page related code
is changed to flush tlb timely.  So we can just remove these local flushing
code.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kvm/mmu/mmu.c     | 5 -----
 arch/x86/kvm/mmu/tdp_mmu.c | 1 -
 2 files changed, 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3c1b069a7bcf..f40087ee2704 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1934,9 +1934,6 @@ static void kvm_mmu_flush_or_zap(struct kvm_vcpu *vcpu,
 {
 	if (kvm_mmu_remote_flush_or_zap(vcpu->kvm, invalid_list, remote_flush))
 		return;
-
-	if (local_flush)
-		kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
 }
 
 #ifdef CONFIG_KVM_MMU_AUDIT
@@ -2144,7 +2141,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 				break;
 
 			WARN_ON(!list_empty(&invalid_list));
-			kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
 		}
 
 		__clear_sp_write_flooding_count(sp);
@@ -2751,7 +2747,6 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	if (set_spte_ret & SET_SPTE_WRITE_PROTECTED_PT) {
 		if (write_fault)
 			ret = RET_PF_EMULATE;
-		kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
 	}
 
 	if (set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH || flush)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 548393c2bfe9..d5339fee6f2d 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -958,7 +958,6 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
 	if (make_spte_ret & SET_SPTE_WRITE_PROTECTED_PT) {
 		if (fault->write)
 			ret = RET_PF_EMULATE;
-		kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
 	}
 
 	/* If a MMIO SPTE is installed, the MMIO will need to be emulated. */
-- 
2.19.1.6.gb485710b