linux-kernel - [PATCH 2/7] KVM: x86: Invoke kvm_mmu_unload() directly on CR4.PCIDE change

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Message-Id: <20211209060552.2956723-3-seanjc@google.com>
Date:   Thu,  9 Dec 2021 06:05:47 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Sean Christopherson <seanjc@...gle.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, Maxim Levitsky <mlevitsk@...hat.com>,
        Ben Gardon <bgardon@...gle.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH 2/7] KVM: x86: Invoke kvm_mmu_unload() directly on CR4.PCIDE change

Replace a KVM_REQ_MMU_RELOAD request with a direct kvm_mmu_unload() call
when the guest's CR4.PCIDE changes.  This will allow tweaking the logic
of KVM_REQ_MMU_RELOAD to free only obsolete/invalid roots, which is the
historical intent of KVM_REQ_MMU_RELOAD.  The recent PCIDE behavior is
the only user of KVM_REQ_MMU_RELOAD that doesn't mark affected roots as
obsolete, needs to unconditionally unload the entire MMU, _and_ affects
only the current vCPU.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1aaf37e1bd0f..ca1f0350a868 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1045,19 +1045,18 @@ void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned lon
 	 * If CR4.PCIDE is changed 0 -> 1, there is no need to flush the TLB
 	 * according to the SDM; however, stale prev_roots could be reused
 	 * incorrectly in the future after a MOV to CR3 with NOFLUSH=1, so we
-	 * free them all.  KVM_REQ_MMU_RELOAD is fit for the both cases; it
-	 * is slow, but changing CR4.PCIDE is a rare case.
+	 * free them all.  kvm_mmu_unload() is fit for the both cases; it is
+	 * slow, but changing CR4.PCIDE is a rare case.
 	 *
 	 * If CR4.PGE is changed, the guest TLB must be flushed.
 	 *
-	 * Note: resetting MMU is a superset of KVM_REQ_MMU_RELOAD and
-	 * KVM_REQ_MMU_RELOAD is a superset of KVM_REQ_TLB_FLUSH_GUEST, hence
-	 * the usage of "else if".
+	 * Note: resetting MMU is a superset of unloading an MMU, and unloading
+	 * an MMU is a superset of KVM_REQ_TLB_FLUSH_GUEST, hence the "else if".
 	 */
 	if ((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS)
 		kvm_mmu_reset_context(vcpu);
 	else if ((cr4 ^ old_cr4) & X86_CR4_PCIDE)
-		kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
+		kvm_mmu_unload(vcpu);
 	else if ((cr4 ^ old_cr4) & X86_CR4_PGE)
 		kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
 }
-- 
2.34.1.400.ga245620fadb-goog