linux-kernel - [PATCH 1/7] KVM: X86/MMU: Add using_special_root

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Date:   Wed, 20 Apr 2022 21:25:59 +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:     Lai Jiangshan <jiangshan.ljs@...group.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 1/7] KVM: X86/MMU: Add using_special_root_page()

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

In some case, special roots are used in mmu.  It is often using
to_shadow_page(mmu->root.hpa) to check if special roots are used.

Add using_special_root_page() to directly check if special roots are
used or needed to be used even mmu->root.hpa is not set.

Prepare for making to_shadow_page(mmu->root.hpa) return !NULL via
using special shadow pages.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kvm/mmu/mmu.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d14cb6f99cb1..6461e499d305 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1714,6 +1714,14 @@ static void drop_parent_pte(struct kvm_mmu_page *sp,
 	mmu_spte_clear_no_track(parent_pte);
 }
 
+static bool using_special_root_page(struct kvm_mmu *mmu)
+{
+	if (mmu->direct_map)
+		return mmu->shadow_root_level == PT32E_ROOT_LEVEL;
+	else
+		return mmu->root_level <= PT32E_ROOT_LEVEL;
+}
+
 static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, int direct)
 {
 	struct kvm_mmu_page *sp;
@@ -4201,10 +4209,10 @@ 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.  Special roots can not be put into
+	 * mmu->prev_root[].
 	 */
-	if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa))
+	if (VALID_PAGE(mmu->root.hpa) && using_special_root_page(mmu))
 		kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT);
 
 	if (VALID_PAGE(mmu->root.hpa))
-- 
2.19.1.6.gb485710b