[PATCH 5.12 107/677] KVM: x86/xen: Drop RAX[63:32] when processing hypercall

[Greg Kroah-Hartman]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

commit 6b48fd4cb206485c357420d91ea766ef81b20dc3 upstream.

Truncate RAX to 32 bits, i.e. consume EAX, when retrieving the hypecall
index for a Xen hypercall.  Per Xen documentation[*], the index is EAX
when the vCPU is not in 64-bit mode.

[*] http://xenbits.xenproject.org/docs/sphinx-unstable/guest-guide/x86/hypercall-abi.html

Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210422022128.3464144-8-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/xen.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -673,7 +673,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *v
 	bool longmode;
 	u64 input, params[6];
 
-	input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);
+	input = (u64)kvm_register_readl(vcpu, VCPU_REGS_RAX);
 
 	/* Hyper-V hypercalls get bit 31 set in EAX */
 	if ((input & 0x80000000) &&