Message-Id: <20210517140242.903613120@linuxfoundation.org>
Date:   Mon, 17 May 2021 16:00:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yu Zhang <yu.c.zhang@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jack Wang <jinpu.wang@...os.com>
Subject: [PATCH 5.4 004/141] KVM: x86/mmu: Remove the defunct update_pte() paging hook

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

commit c5e2184d1544f9e56140791eff1a351bea2e63b9 upstream.

Remove the update_pte() shadow paging logic, which was obsoleted by
commit 4731d4c7a077 ("KVM: MMU: out of sync shadow core"), but never
removed.  As pointed out by Yu, KVM never write protects leaf page
tables for the purposes of shadow paging, and instead marks their
associated shadow page as unsync so that the guest can write PTEs at
will.

The update_pte() path, which predates the unsync logic, optimizes COW
scenarios by refreshing leaf SPTEs when they are written, as opposed to
zapping the SPTE, restarting the guest, and installing the new SPTE on
the subsequent fault.  Since KVM no longer write-protects leaf page
tables, update_pte() is unreachable and can be dropped.

Reported-by: Yu Zhang <yu.c.zhang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20210115004051.4099250-1-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
(jwang: backport to 5.4 to fix a warning on AMD nested Virtualization)
Signed-off-by: Jack Wang <jinpu.wang@...os.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/asm/kvm_host.h |    3 ---
 arch/x86/kvm/mmu.c              |   33 ++-------------------------------
 arch/x86/kvm/x86.c              |    1 -
 3 files changed, 2 insertions(+), 35 deletions(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -391,8 +391,6 @@ struct kvm_mmu {
 	int (*sync_page)(struct kvm_vcpu *vcpu,
 			 struct kvm_mmu_page *sp);
 	void (*invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa);
-	void (*update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
-			   u64 *spte, const void *pte);
 	hpa_t root_hpa;
 	gpa_t root_cr3;
 	union kvm_mmu_role mmu_role;
@@ -944,7 +942,6 @@ struct kvm_arch {
 struct kvm_vm_stat {
 	ulong mmu_shadow_zapped;
 	ulong mmu_pte_write;
-	ulong mmu_pte_updated;
 	ulong mmu_pde_zapped;
 	ulong mmu_flooded;
 	ulong mmu_recycled;
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2243,13 +2243,6 @@ static void nonpaging_invlpg(struct kvm_
 {
 }
 
-static void nonpaging_update_pte(struct kvm_vcpu *vcpu,
-				 struct kvm_mmu_page *sp, u64 *spte,
-				 const void *pte)
-{
-	WARN_ON(1);
-}
-
 #define KVM_PAGE_ARRAY_NR 16
 
 struct kvm_mmu_pages {
@@ -4356,7 +4349,6 @@ static void nonpaging_init_context(struc
 	context->gva_to_gpa = nonpaging_gva_to_gpa;
 	context->sync_page = nonpaging_sync_page;
 	context->invlpg = nonpaging_invlpg;
-	context->update_pte = nonpaging_update_pte;
 	context->root_level = 0;
 	context->shadow_root_level = PT32E_ROOT_LEVEL;
 	context->direct_map = true;
@@ -4935,7 +4927,6 @@ static void paging64_init_context_common
 	context->gva_to_gpa = paging64_gva_to_gpa;
 	context->sync_page = paging64_sync_page;
 	context->invlpg = paging64_invlpg;
-	context->update_pte = paging64_update_pte;
 	context->shadow_root_level = level;
 	context->direct_map = false;
 }
@@ -4964,7 +4955,6 @@ static void paging32_init_context(struct
 	context->gva_to_gpa = paging32_gva_to_gpa;
 	context->sync_page = paging32_sync_page;
 	context->invlpg = paging32_invlpg;
-	context->update_pte = paging32_update_pte;
 	context->shadow_root_level = PT32E_ROOT_LEVEL;
 	context->direct_map = false;
 }
@@ -5039,7 +5029,6 @@ static void init_kvm_tdp_mmu(struct kvm_
 	context->page_fault = tdp_page_fault;
 	context->sync_page = nonpaging_sync_page;
 	context->invlpg = nonpaging_invlpg;
-	context->update_pte = nonpaging_update_pte;
 	context->shadow_root_level = kvm_x86_ops->get_tdp_level(vcpu);
 	context->direct_map = true;
 	context->set_cr3 = kvm_x86_ops->set_tdp_cr3;
@@ -5172,7 +5161,6 @@ void kvm_init_shadow_ept_mmu(struct kvm_
 	context->gva_to_gpa = ept_gva_to_gpa;
 	context->sync_page = ept_sync_page;
 	context->invlpg = ept_invlpg;
-	context->update_pte = ept_update_pte;
 	context->root_level = PT64_ROOT_4LEVEL;
 	context->direct_map = false;
 	context->mmu_role.as_u64 = new_role.as_u64;
@@ -5312,19 +5300,6 @@ void kvm_mmu_unload(struct kvm_vcpu *vcp
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_unload);
 
-static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
-				  struct kvm_mmu_page *sp, u64 *spte,
-				  const void *new)
-{
-	if (sp->role.level != PT_PAGE_TABLE_LEVEL) {
-		++vcpu->kvm->stat.mmu_pde_zapped;
-		return;
-        }
-
-	++vcpu->kvm->stat.mmu_pte_updated;
-	vcpu->arch.mmu->update_pte(vcpu, sp, spte, new);
-}
-
 static bool need_remote_flush(u64 old, u64 new)
 {
 	if (!is_shadow_present_pte(old))
@@ -5490,14 +5465,10 @@ static void kvm_mmu_pte_write(struct kvm
 
 		local_flush = true;
 		while (npte--) {
-			u32 base_role = vcpu->arch.mmu->mmu_role.base.word;
-
 			entry = *spte;
 			mmu_page_zap_pte(vcpu->kvm, sp, spte);
-			if (gentry &&
-			      !((sp->role.word ^ base_role)
-			      & mmu_base_role_mask.word) && rmap_can_add(vcpu))
-				mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
+			if (gentry && sp->role.level != PG_LEVEL_4K)
+				++vcpu->kvm->stat.mmu_pde_zapped;
 			if (need_remote_flush(entry, *spte))
 				remote_flush = true;
 			++spte;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -208,7 +208,6 @@ struct kvm_stats_debugfs_item debugfs_en
 	{ "l1d_flush", VCPU_STAT(l1d_flush) },
 	{ "mmu_shadow_zapped", VM_STAT(mmu_shadow_zapped) },
 	{ "mmu_pte_write", VM_STAT(mmu_pte_write) },
-	{ "mmu_pte_updated", VM_STAT(mmu_pte_updated) },
 	{ "mmu_pde_zapped", VM_STAT(mmu_pde_zapped) },
 	{ "mmu_flooded", VM_STAT(mmu_flooded) },
 	{ "mmu_recycled", VM_STAT(mmu_recycled) },

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