linux-kernel - [PATCH v7 2/4] KVM: x86: report negative values from wrmsr emulation to userspace

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Date:   Thu,  1 Oct 2020 14:29:52 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v7 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 | 4 ++--
 arch/x86/kvm/x86.c     | 9 ++++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0cc0db500f718..0d917eb703194 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3712,10 +3712,10 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
 	if (r == X86EMUL_IO_NEEDED)
 		return r;
 
-	if (r)
+	if (r > 0)
 		return emulate_gp(ctxt, 0);
 
-	return X86EMUL_CONTINUE;
+	return r < 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 09a0cad49af51..7af04f9e20b48 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1737,13 +1737,16 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
 	r = kvm_set_msr(vcpu, ecx, data);
 
 	/* MSR write failed? See if we should ask user space */
-	if (r && kvm_set_msr_user_space(vcpu, ecx, data, r)) {
+	if (r && kvm_set_msr_user_space(vcpu, ecx, data, r))
 		/* Bounce to user space */
 		return 0;
-	}
+
+	/* Signal all other negative errors to userspace */
+	if (r < 0)
+		return r;
 
 	/* MSR write failed? Inject a #GP */
-	if (r) {
+	if (r > 0) {
 		trace_kvm_msr_write_ex(ecx, data);
 		kvm_inject_gp(vcpu, 0);
 		return 1;
-- 
2.26.2