linux-kernel - [PATCH 08/14] KVM: x86/mmu: Drop level optimization from fast_page

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Date:   Wed,  8 Jan 2020 12:24:42 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Paul Mackerras <paulus@...abs.org>,
        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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        syzbot+c9d1fb51ac9d0d10c39d@...kaller.appspotmail.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Barret Rhoden <brho@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Jason Zeng <jason.zeng@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: [PATCH 08/14] KVM: x86/mmu: Drop level optimization from fast_page_fault()

Remove fast_page_fault()'s optimization to stop the shadow walk if the
iterator level drops below the intended map level.  The intended map
level is only acccurate for HugeTLB mappings (THP mappings are detected
after fast_page_fault()), i.e. it's not required for correctness, and
a future patch will also move HugeTLB mapping detection to after
fast_page_fault().

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4bd7f745b56d..7d78d1d996ed 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3593,7 +3593,7 @@ static bool is_access_allowed(u32 fault_err_code, u64 spte)
  * - true: let the vcpu to access on the same address again.
  * - false: let the real page fault path to fix it.
  */
-static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, int level,
+static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    u32 error_code)
 {
 	struct kvm_shadow_walk_iterator iterator;
@@ -3611,8 +3611,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, int level,
 		u64 new_spte;
 
 		for_each_shadow_entry_lockless(vcpu, cr2_or_gpa, iterator, spte)
-			if (!is_shadow_present_pte(spte) ||
-			    iterator.level < level)
+			if (!is_shadow_present_pte(spte))
 				break;
 
 		sp = page_header(__pa(iterator.sptep));
@@ -4223,7 +4222,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	if (level > PT_PAGE_TABLE_LEVEL)
 		gfn &= ~(KVM_PAGES_PER_HPAGE(level) - 1);
 
-	if (fast_page_fault(vcpu, gpa, level, error_code))
+	if (fast_page_fault(vcpu, gpa, error_code))
 		return RET_PF_RETRY;
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
-- 
2.24.1