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

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Date:   Wed, 12 May 2021 16:42:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Joao Martins <joao.m.martins@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.12 107/677] KVM: x86/xen: Drop RAX[63:32] when processing hypercall

From: Sean Christopherson <seanjc@...gle.com>

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@...cle.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20210422022128.3464144-8-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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) &&