linux-kernel - [PATCH V3 02/12] KVM: X86/MMU: Add using_local_root

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Date:   Sat, 21 May 2022 21:16:50 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>
Subject: [PATCH V3 02/12] KVM: X86/MMU: Add using_local_root_page()

From: Lai Jiangshan <jiangshan.ljs@...group.com>

In some cases, local root pages are used for MMU.  It is often using
to_shadow_page(mmu->root.hpa) to check if local root pages are used.

Add using_local_root_page() to directly check if local root pages are
used or needed to be used even mmu->root.hpa is not set.

Prepare for making to_shadow_page(mmu->root.hpa) returns non-NULL via
using local shadow [root] pages.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kvm/mmu/mmu.c | 40 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index efe5a3dca1e0..624b6d2473f7 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1690,6 +1690,39 @@ static void drop_parent_pte(struct kvm_mmu_page *sp,
 	mmu_spte_clear_no_track(parent_pte);
 }
 
+/*
+ * KVM uses the VCPU's local root page (vcpu->mmu->pae_root) when either the
+ * shadow pagetable is using PAE paging or the host is shadowing nested NPT for
+ * 32bit L1 hypervisor.
+ *
+ * It includes cases:
+ *	nonpaging when !tdp_enabled				(direct paging)
+ *	shadow paging for 32 bit guest when !tdp_enabled	(shadow paging)
+ *	NPT in 32bit host (not shadowing nested NPT)		(direct paging)
+ *	shadow nested NPT for 32bit L1 hypervisor in 32bit host (shadow paging)
+ *	shadow nested NPT for 32bit L1 hypervisor in 64bit host (shadow paging)
+ *
+ * For the first four cases, mmu->root_role.level is PT32E_ROOT_LEVEL and the
+ * shadow pagetable is using PAE paging.
+ *
+ * For the last case, it is
+ * 	mmu->root_role.level > PT32E_ROOT_LEVEL &&
+ * 	!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL
+ * And if this condition is true, it must be the last case.
+ *
+ * With the two conditions combined, the checking condition is:
+ * 	mmu->root_role.level == PT32E_ROOT_LEVEL ||
+ * 	(!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL)
+ *
+ * (There is no "mmu->root_role.level > PT32E_ROOT_LEVEL" here, because it is
+ *  already ensured that mmu->root_role.level >= PT32E_ROOT_LEVEL)
+ */
+static bool using_local_root_page(struct kvm_mmu *mmu)
+{
+	return mmu->root_role.level == PT32E_ROOT_LEVEL ||
+	       (!mmu->root_role.direct && mmu->cpu_role.base.level <= PT32E_ROOT_LEVEL);
+}
+
 static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, int direct)
 {
 	struct kvm_mmu_page *sp;
@@ -4252,10 +4285,11 @@ static bool fast_pgd_switch(struct kvm *kvm, struct kvm_mmu *mmu,
 {
 	/*
 	 * For now, limit the caching to 64-bit hosts+VMs in order to avoid
-	 * having to deal with PDPTEs. We may add support for 32-bit hosts/VMs
-	 * later if necessary.
+	 * having to deal with PDPTEs.  Local roots can not be put into
+	 * mmu->prev_roots[] because mmu->pae_root can not be shared for
+	 * different roots at the same time.
 	 */
-	if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa))
+	if (unlikely(using_local_root_page(mmu)))
 		kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT);
 
 	if (VALID_PAGE(mmu->root.hpa))
-- 
2.19.1.6.gb485710b