linux-kernel - [PATCH v6 2/4] KVM: x86: report negative values from wrmsr emulation to userspace

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Message-Id: <20200922211025.175547-3-mlevitsk@redhat.com>
Date:   Wed, 23 Sep 2020 00:10:23 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v6 2/4] KVM: x86: report negative values from wrmsr emulation to userspace

This will allow the KVM to report such errors (e.g -ENOMEM)
to the userspace.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/emulate.c | 7 +++++--
 arch/x86/kvm/x86.c     | 6 +++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 1d450d7710d63..d855304f5a509 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3702,13 +3702,16 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt)
 static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
 {
 	u64 msr_data;
+	int ret;
 
 	msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX)
 		| ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32);
-	if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data))
+
+	ret = ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data);
+	if (ret > 0)
 		return emulate_gp(ctxt, 0);
 
-	return X86EMUL_CONTINUE;
+	return ret < 0 ? X86EMUL_UNHANDLEABLE : X86EMUL_CONTINUE;
 }
 
 static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 063d70e736f7f..e4b07be450d4e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1612,8 +1612,12 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
 {
 	u32 ecx = kvm_rcx_read(vcpu);
 	u64 data = kvm_read_edx_eax(vcpu);
+	int ret = kvm_set_msr(vcpu, ecx, data);
 
-	if (kvm_set_msr(vcpu, ecx, data)) {
+	if (ret < 0)
+		return ret;
+
+	if (ret > 0) {
 		trace_kvm_msr_write_ex(ecx, data);
 		kvm_inject_gp(vcpu, 0);
 		return 1;
-- 
2.26.2