[PATCH] kvm: always set accessed bit in VMCS segment selectors

[Andre Przywara <andre.przywara@amd.com>]

Intel manual 22.3.1.2 demands that the accessed bit (bit 0 in type field)
must be set when on DS,ES,FS and GS when the selector is usable.
This fixes cross vendor migration from AMD to Intel.

I am not sure what the real purpose of this check is, so I put this
in the VMX path and not in the SVM one. If someone has an explanation
which justifies a move, I am happy to do this.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 arch/x86/kvm/vmx.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9b56d21..d19e39c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1723,6 +1723,11 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu,
 		ar = 0xf3;
 	} else
 		ar = vmx_segment_access_rights(var);
+
+	/* 22.3.1.2 demands that the accessed bit must be set on [DEFG]S */
+	if (var->s && (sf->ar_bytes & AR_UNUSABLE_MASK) == 0)
+		ar |= 0x1;
+
 	vmcs_write32(sf->ar_bytes, ar);
 }
 
-- 
1.5.2.2