Patch "KVM: x86: fix RSM into 64-bit protected mode" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: fix RSM into 64-bit protected mode

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     kvm-x86-fix-rsm-into-64-bit-protected-mode.patch

and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paolo Bonzini <[email protected]>
Date: Wed, 14 Oct 2015 15:25:52 +0200
Subject: KVM: x86: fix RSM into 64-bit protected mode

From: Paolo Bonzini <[email protected]>

commit b10d92a54dac25a6152f1aa1ffc95c12908035ce upstream.

In order to get into 64-bit protected mode, you need to enable paging while EFER.LMA=1. For this to work, CS.L must be 0. Currently, we load the segments before CR0 and CR4, which means that if RSM returns into 64-bit protected mode CS.L is already 1 and everything breaks.

Luckily, CS.L=0 is always the case when executing RSM, because it is forbidden to execute RSM from 64-bit protected mode. Hence it is enough to load CR0 and CR4 first, and only then the segments.

---
 arch/x86/kvm/emulate.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

@@ -2418,7 +2418,7 @@ static int rsm_load_state_64(struct x86_
 	u64 val, cr0, cr4;
 	u32 base3;
 	u16 selector;
-	int i;
+	int i, r;
 
 	for (i = 0; i < 16; i++)
 		*reg_write(ctxt, i) = GET_SMSTATE(u64, smbase, 0x7ff8 - i * 8);

@@ -2460,13 +2460,17 @@ static int rsm_load_state_64(struct x86_
 	dt.address =                GET_SMSTATE(u64, smbase, 0x7e68);
 	ctxt->ops->set_gdt(ctxt, &dt);
 
+	r = rsm_enter_protected_mode(ctxt, cr0, cr4);
+	if (r != X86EMUL_CONTINUE)
+		return r;
+
 	for (i = 0; i < 6; i++) {
-		int r = rsm_load_seg_64(ctxt, smbase, i);
+		r = rsm_load_seg_64(ctxt, smbase, i);
 		if (r != X86EMUL_CONTINUE)
 			return r;
 	}
 
-	return rsm_enter_protected_mode(ctxt, cr0, cr4);
+	return X86EMUL_CONTINUE;
 }
 
 static int em_rsm(struct x86_emulate_ctxt *ctxt)

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/kvm-x86-fix-smi-to-halted-vcpu.patch queue-4.2/kvm-x86-clean-up-kvm_arch_vcpu_runnable.patch queue-4.2/kvm-x86-fix-rsm-into-64-bit-protected-mode.patch