linux-kernel - [PATCH 8/9] KVM: x86: Drop .post_leave_smm(), i.e. the manual post-RSM MMU reset

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Message-Id: <20210609185619.992058-9-seanjc@google.com>
Date:   Wed,  9 Jun 2021 11:56:18 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     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,
        syzbot+fb0b6a7e8713aeb0319c@...kaller.appspotmail.com
Subject: [PATCH 8/9] KVM: x86: Drop .post_leave_smm(), i.e. the manual
 post-RSM MMU reset

Drop the .post_leave_smm() emulator callback, which at this point is just
a wrapper to kvm_mmu_reset_context().  The manual context reset is
unnecessary, because unlike enter_smm() which calls vendor MSR/CR helpers
directly, em_rsm() bounces through the KVM helpers, e.g. kvm_set_cr4(),
which are responsible for processing side effects.  em_rsm() is already
subtly relying on this behavior as it doesn't manually do
kvm_update_cpuid_runtime(), e.g. to recognize CR4.OSXSAVE changes.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/emulate.c     | 10 ++++++++--
 arch/x86/kvm/kvm_emulate.h |  1 -
 arch/x86/kvm/x86.c         |  6 ------
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 9e0d5900c011..34c9f785d715 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2694,8 +2694,14 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
 	if (ret != X86EMUL_CONTINUE)
 		goto emulate_shutdown;
 
-	ctxt->ops->post_leave_smm(ctxt);
-
+	/*
+	 * Note, the ctxt->ops callbacks are responsible for handling side
+	 * effects when writing MSRs and CRs, e.g. MMU context resets, CPUID
+	 * runtime updates, etc...  If that changes, e.g. this flow is moved
+	 * out of the emulator to make it look more like enter_smm(), then
+	 * those side effects need to be explicitly handled for both success
+	 * and shutdown.
+	 */
 	return X86EMUL_CONTINUE;
 
 emulate_shutdown:
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index b620782c1fb5..31dc7ca4ff2b 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -232,7 +232,6 @@ struct x86_emulate_ops {
 	void (*exiting_smm)(struct x86_emulate_ctxt *ctxt);
 	int (*pre_leave_smm)(struct x86_emulate_ctxt *ctxt,
 			     const char *smstate);
-	void (*post_leave_smm)(struct x86_emulate_ctxt *ctxt);
 	void (*triple_fault)(struct x86_emulate_ctxt *ctxt);
 	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
 };
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 06f3be2d170b..347849caf1df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7112,11 +7112,6 @@ static int emulator_pre_leave_smm(struct x86_emulate_ctxt *ctxt,
 	return static_call(kvm_x86_pre_leave_smm)(emul_to_vcpu(ctxt), smstate);
 }
 
-static void emulator_post_leave_smm(struct x86_emulate_ctxt *ctxt)
-{
-	kvm_mmu_reset_context(emul_to_vcpu(ctxt));
-}
-
 static void emulator_triple_fault(struct x86_emulate_ctxt *ctxt)
 {
 	kvm_make_request(KVM_REQ_TRIPLE_FAULT, emul_to_vcpu(ctxt));
@@ -7170,7 +7165,6 @@ static const struct x86_emulate_ops emulate_ops = {
 	.get_hflags          = emulator_get_hflags,
 	.exiting_smm         = emulator_exiting_smm,
 	.pre_leave_smm       = emulator_pre_leave_smm,
-	.post_leave_smm      = emulator_post_leave_smm,
 	.triple_fault        = emulator_triple_fault,
 	.set_xcr             = emulator_set_xcr,
 };
-- 
2.32.0.rc1.229.g3e70b5a671-goog