linux-kernel - [PATCH] KVM: x86/mmu: Fix MMU role calculation to not drop level

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Date:   Sat, 29 Feb 2020 15:11:22 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...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] KVM: x86/mmu: Fix MMU role calculation to not drop level

Use the calculated role as-is when propagating it to kvm_mmu.mmu_role,
i.e. stop masking off meaningful fields.  The concept of masking off
fields came from kvm_mmu_pte_write(), which (correctly) ignores certain
fields when comparing kvm_mmu_page.role against kvm_mmu.mmu_role, e.g.
the current mmu's access and level have no relation to a shadow page's
access and level.

This fixes a bug where KVM will fail to reset shadow_root_level and
root_level when L1 switches from running L2 with 5-level to running L2
with 4-level.

Opportunistically rework the mask for kvm_mmu_pte_write() to define the
fields that should be ignored as opposed to the fields that should be
checked, i.e. make it opt-out instead of opt-in so that new fields are
automatically picked up.  While doing so, stop ignoring "direct".  The
field is effectively ignored anyways because kvm_mmu_pte_write() is only
reached with an indirect mmu and the loop only walks indirect shadow
pages, but double checking "direct" literally costs nothing.

Fixes: 9fa72119b24d ("kvm: x86: Introduce kvm_mmu_calc_root_page_role()")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/mmu.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c4e0b97f82ac..80b21b7cf092 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -215,17 +215,6 @@ struct kvm_shadow_walk_iterator {
 	unsigned index;
 };
 
-static const union kvm_mmu_page_role mmu_base_role_mask = {
-	.cr0_wp = 1,
-	.gpte_is_8_bytes = 1,
-	.nxe = 1,
-	.smep_andnot_wp = 1,
-	.smap_andnot_wp = 1,
-	.smm = 1,
-	.guest_mode = 1,
-	.ad_disabled = 1,
-};
-
 #define for_each_shadow_entry_using_root(_vcpu, _root, _addr, _walker)     \
 	for (shadow_walk_init_using_root(&(_walker), (_vcpu),              \
 					 (_root), (_addr));                \
@@ -4919,7 +4908,6 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 	union kvm_mmu_role new_role =
 		kvm_calc_tdp_mmu_root_page_role(vcpu, false);
 
-	new_role.base.word &= mmu_base_role_mask.word;
 	if (new_role.as_u64 == context->mmu_role.as_u64)
 		return;
 
@@ -4991,7 +4979,6 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
 	union kvm_mmu_role new_role =
 		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
 
-	new_role.base.word &= mmu_base_role_mask.word;
 	if (new_role.as_u64 == context->mmu_role.as_u64)
 		return;
 
@@ -5048,7 +5035,6 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 
 	__kvm_mmu_new_cr3(vcpu, new_eptp, new_role.base, false);
 
-	new_role.base.word &= mmu_base_role_mask.word;
 	if (new_role.as_u64 == context->mmu_role.as_u64)
 		return;
 
@@ -5089,7 +5075,6 @@ static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
 	union kvm_mmu_role new_role = kvm_calc_mmu_role_common(vcpu, false);
 	struct kvm_mmu *g_context = &vcpu->arch.nested_mmu;
 
-	new_role.base.word &= mmu_base_role_mask.word;
 	if (new_role.as_u64 == g_context->mmu_role.as_u64)
 		return;
 
@@ -5328,6 +5313,22 @@ static u64 *get_written_sptes(struct kvm_mmu_page *sp, gpa_t gpa, int *nspte)
 	return spte;
 }
 
+/*
+ * Ignore various flags when determining if a SPTE can be immediately
+ * overwritten for the current MMU.
+ *  - level: explicitly checked in mmu_pte_write_new_pte(), and will never
+ *    match the current MMU role, as MMU's level tracks the root level.
+ *  - access: updated based on the new guest PTE
+ *  - quadrant: handled by get_written_sptes()
+ *  - invalid: always false (loop only walks valid shadow pages)
+ */
+static const union kvm_mmu_page_role role_ign = {
+	.level = 0xf,
+	.access = 0x7,
+	.quadrant = 0x3,
+	.invalid = 0x1,
+};
+
 static void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 			      const u8 *new, int bytes,
 			      struct kvm_page_track_notifier_node *node)
@@ -5383,8 +5384,8 @@ static void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 			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))
+			    !((sp->role.word ^ base_role) & ~role_ign.word) &&
+			    rmap_can_add(vcpu))
 				mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
 			if (need_remote_flush(entry, *spte))
 				remote_flush = true;
-- 
2.24.1