From: Jan Beulich <jbeulich@suse.com>
Date: Wed, 19 Apr 2017 11:24:18 +0000 (+0200)
Subject: x86emul: add "unblock NMI" retire flag
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~2224
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=75704266f987c11ed98cd0a26c52898ab358e95e;p=xen.git

x86emul: add "unblock NMI" retire flag

No matter that we emulate IRET for (guest) real mode only right now, we
should get its effect on (virtual) NMI delivery right. Note that we can
simply check the other retire flags also in the !OKAY case, as the
insn emulator now guarantees them to only be set on OKAY.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>
---

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 91e269f80f..612c1f9e9a 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -1955,9 +1955,6 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt,
         memcpy(vio->mmio_insn, hvmemul_ctxt->insn_buf, vio->mmio_insn_bytes);
     }
 
-    if ( rc != X86EMUL_OKAY )
-        return rc;
-
     if ( hvmemul_ctxt->ctxt.retire.singlestep )
         hvm_inject_hw_exception(TRAP_debug, X86_EVENT_NO_EC);
 
@@ -1966,15 +1963,19 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt,
     /* MOV-SS instruction toggles MOV-SS shadow, else we just clear it. */
     if ( hvmemul_ctxt->ctxt.retire.mov_ss )
         new_intr_shadow ^= HVM_INTR_SHADOW_MOV_SS;
-    else
+    else if ( rc != X86EMUL_RETRY )
         new_intr_shadow &= ~HVM_INTR_SHADOW_MOV_SS;
 
     /* STI instruction toggles STI shadow, else we just clear it. */
     if ( hvmemul_ctxt->ctxt.retire.sti )
         new_intr_shadow ^= HVM_INTR_SHADOW_STI;
-    else
+    else if ( rc != X86EMUL_RETRY )
         new_intr_shadow &= ~HVM_INTR_SHADOW_STI;
 
+    /* IRET, if valid in the given context, clears NMI blocking. */
+    if ( hvmemul_ctxt->ctxt.retire.unblock_nmi )
+        new_intr_shadow &= ~HVM_INTR_SHADOW_NMI;
+
     if ( hvmemul_ctxt->intr_shadow != new_intr_shadow )
     {
         hvmemul_ctxt->intr_shadow = new_intr_shadow;
@@ -1987,7 +1988,7 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt,
         hvm_hlt(regs->eflags);
     }
 
-    return X86EMUL_OKAY;
+    return rc;
 }
 
 int hvm_emulate_one(
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index c32fe2d841..6f1076148e 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4002,6 +4002,7 @@ x86_emulate(
         uint32_t mask = X86_EFLAGS_VIP | X86_EFLAGS_VIF | X86_EFLAGS_VM;
 
         fail_if(!in_realmode(ctxt, ops));
+        ctxt->retire.unblock_nmi = true;
         if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
                               &eip, op_bytes, ctxt, ops)) ||
              (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
@@ -7918,9 +7919,17 @@ int x86_emulate_wrapper(
 
     rc = x86_emulate(ctxt, ops);
 
-    /* Retire flags should only be set for successful instruction emulation. */
+    /*
+     * Most retire flags should only be set for successful instruction
+     * emulation.
+     */
     if ( rc != X86EMUL_OKAY )
-        ASSERT(ctxt->retire.raw == 0);
+    {
+        typeof(ctxt->retire) retire = ctxt->retire;
+
+        retire.unblock_nmi = false;
+        ASSERT(!retire.raw);
+    }
 
     /* All cases returning X86EMUL_EXCEPTION should have fault semantics. */
     if ( rc == X86EMUL_EXCEPTION )
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h b/xen/arch/x86/x86_emulate/x86_emulate.h
index d9a252eac1..e5ec8a6122 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -490,6 +490,7 @@ struct x86_emulate_ctxt
             bool hlt:1;          /* Instruction HLTed. */
             bool mov_ss:1;       /* Instruction sets MOV-SS irq shadow. */
             bool sti:1;          /* Instruction sets STI irq shadow. */
+            bool unblock_nmi:1;  /* Instruction clears NMI blocking. */
             bool singlestep:1;   /* Singlestepping was active. */
         };
     } retire;