From: Jan Beulich <jbeulich@suse.com>
Date: Fri, 16 Mar 2018 16:27:36 +0000 (+0100)
Subject: x86: correct EFLAGS.IF in SYSENTER frame
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~388
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=c4dd58f0cf23cdf119bbccedfb8c24435fc6f3ab;p=xen.git

x86: correct EFLAGS.IF in SYSENTER frame

Commit 9d1d31ad94 ("x86: slightly reduce Meltdown band-aid overhead")
moved the STI past the PUSHF. While this isn't an active problem (as we
force EFLAGS.IF to 1 before exiting to guest context), let's not risk
internal confusion by finding a PV guest frame with interrupts
apparently off.

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

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index f6ba31c4e2..e3d18daba8 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -281,6 +281,8 @@ GLOBAL(sysenter_eflags_saved)
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         GET_STACK_END(bx)
+        /* PUSHF above has saved EFLAGS.IF clear (the caller had it set). */
+        orl   $X86_EFLAGS_IF, UREGS_eflags(%rsp)
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
         neg   %rcx
         jz    .Lsyse_cr3_okay