linux-kernel - [PATCH 08/16] KVM: x86/mmu: Incorporate guest's page level into max level for shadow MMU

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Date:   Fri,  6 Dec 2019 15:57:21 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...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
Subject: [PATCH 08/16] KVM: x86/mmu: Incorporate guest's page level into max level for shadow MMU

Restrict the max level for a shadow page based on the guest's level
instead of capping the level after the fact for host-mapped huge pages,
e.g. hugetlbfs pages.  Explicitly capping the max level using the guest
mapping level also eliminates FNAME(page_fault)'s subtle dependency on
THP only supporting 2mb pages.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 1938a6e4e631..7d57ec576df0 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -773,7 +773,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 	struct guest_walker walker;
 	int r;
 	kvm_pfn_t pfn;
-	int level = PT_PAGE_TABLE_LEVEL;
+	int level;
 	unsigned long mmu_seq;
 	bool map_writable, is_self_change_mapping;
 	bool lpage_disallowed = (error_code & PFERR_FETCH_MASK) &&
@@ -818,18 +818,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 	is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu,
 	      &walker, user_fault, &vcpu->arch.write_fault_to_shadow_pgtable);
 
-	max_level = lpage_disallowed ? PT_PAGE_TABLE_LEVEL :
-				       PT_MAX_HUGEPAGE_LEVEL;
-
-	if (walker.level >= PT_DIRECTORY_LEVEL && !is_self_change_mapping) {
-		level = mapping_level(vcpu, walker.gfn, &max_level);
-		if (likely(max_level > PT_DIRECTORY_LEVEL)) {
-			level = min(walker.level, level);
-			walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
-		}
-	} else {
+	if (lpage_disallowed || is_self_change_mapping)
 		max_level = PT_PAGE_TABLE_LEVEL;
-	}
+	else
+		max_level = walker.level;
+
+	level = mapping_level(vcpu, walker.gfn, &max_level);
+	if (level > PT_PAGE_TABLE_LEVEL)
+		walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
-- 
2.24.0