From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 28 Jun 2018 07:08:04 +0000 (+0200)
Subject: x86: guard against #NM
X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~3735
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=00cebd6f22beb6d5fa65ed2d8d1ff9acf59bce61;p=xen.git

x86: guard against #NM

Just in case we still don't get CR0.TS handling right, prevent a host
crash by honoring exception fixups in do_device_not_available(). This
would in particular cover emulator stubs raising #NM.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 3e05cf172c..9f045a2045 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1749,7 +1749,21 @@ void do_device_not_available(struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
 
-    BUG_ON(!guest_mode(regs));
+    if ( !guest_mode(regs) )
+    {
+        unsigned long fixup = search_exception_table(regs);
+
+        gprintk(XENLOG_ERR, "#NM: %p [%ps] -> %p\n",
+                _p(regs->rip), _p(regs->rip), _p(fixup));
+        /*
+         * We shouldn't be able to reach here, but for release builds have
+         * the recovery logic in place nevertheless.
+         */
+        ASSERT_UNREACHABLE();
+        BUG_ON(!fixup);
+        regs->rip = fixup;
+        return;
+    }
 
     vcpu_restore_fpu_lazy(curr);