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>
Release-acked-by: Juergen Gross <jgross@suse.com>
master commit: 00cebd6f22beb6d5fa65ed2d8d1ff9acf59bce61
master date: 2018-06-28 09:08:04 +0200

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 3e05cf172ce4b75b24da6a7c6ba4403fa999e221..9f045a2045a2f57af8a74e98444cfeac805f3e81 100644 (file)
--- 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);