[PATCH v2 7/9] KVM: x86/xen: Drop RAX[63:32] when processing hypercall

Sean Christopherson
2021-04-22T02:21:50Z

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@oracle.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/xen.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index ae17250e1efe..7f27bb65a572 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -673,7 +673,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
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) &&