Re: [PATCH] KVM: x86: Revert "check CS.DPL against RPL during task switch"

[Paolo Bonzini <pbonzini@redhat.com>]

Il 17/08/2014 21:32, Nadav Amit ha scritto:
> This reverts commit 5045b468037dfe1c848827ce10e99d87f5669160.  Although the
> cs.dpl=cs.rpl check is mentioned in table 7-1 of the SDM as causing a #TSS
> exception, it is not mentioned in table 6-6 that lists "invalid TSS conditions"
> which cause #TSS exceptions. As it causes some tests, which pass on bare-metal,
> to fail - it should be reverted.

Right.  However, I think reverting the patch is too big a hammer.  We 
still need in_task_switch to raise TS_VECTOR instead of GP_VECTOR, so I 
propose instead something like:

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 56657b0bb3bb..cd230b035514 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1468,7 +1468,7 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 		return ret;
 
 	err_code = selector & 0xfffc;
-	err_vec = GP_VECTOR;
+	err_vec = in_task_switch ? TS_VECTOR : GP_VECTOR;
 
 	/* can't load system descriptor into segment selector */
 	if (seg <= VCPU_SREG_GS && !seg_desc.s)
@@ -1491,9 +1491,6 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 			goto exception;
 		break;
 	case VCPU_SREG_CS:
-		if (in_task_switch && rpl != dpl)
-			goto exception;
-
 		if (!(seg_desc.type & 8))
 			goto exception;
 

either in a single patch or as two separate patch.  I'll test this against
your test case and repost (not before Tuesday).

Paolo