linux-kernel - [PATCH 1/4] KVM: x86: hyper-v: Check access to hypercall before reading XMM registers

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Message-Id: <20210730122625.112848-2-vkuznets@redhat.com>
Date:   Fri, 30 Jul 2021 14:26:22 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] KVM: x86: hyper-v: Check access to hypercall before reading XMM registers

In case guest doesn't have access to the particular hypercall we can avoid
reading XMM registers.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/hyperv.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index b07592ca92f0..cb7e045905a5 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2173,9 +2173,6 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	hc.rep_idx = (hc.param >> HV_HYPERCALL_REP_START_OFFSET) & 0xfff;
 	hc.rep = !!(hc.rep_cnt || hc.rep_idx);
 
-	if (hc.fast && is_xmm_fast_hypercall(&hc))
-		kvm_hv_hypercall_read_xmm(&hc);
-
 	trace_kvm_hv_hypercall(hc.code, hc.fast, hc.rep_cnt, hc.rep_idx,
 			       hc.ingpa, hc.outgpa);
 
@@ -2184,6 +2181,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 		goto hypercall_complete;
 	}
 
+	if (hc.fast && is_xmm_fast_hypercall(&hc))
+		kvm_hv_hypercall_read_xmm(&hc);
+
 	switch (hc.code) {
 	case HVCALL_NOTIFY_LONG_SPIN_WAIT:
 		if (unlikely(hc.rep)) {
-- 
2.31.1