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From 2f6d988d14532616d1f1f476b438b4e3295329f1 Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson@redhat.com>
Date: Fri, 10 Apr 2015 16:45:59 +0200
Subject: [PATCH 13/14] x86: Clear MTRRs on vCPU reset

Message-id: <20150410164559.16166.37319.stgit@gimli.home>
Patchwork-id: 64799
O-Subject: [RHEL7.2 qemu-kvm PATCH 3/3] x86: Clear MTRRs on vCPU reset
Bugzilla: 1210510
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Upstream: 9db2efd95e13330075bff027cd682a063d725332

The SDM specifies (June 2014 Vol3 11.11.5):

    On a hardware reset, the P6 and more recent processors clear the
    valid flags in variable-range MTRRs and clear the E flag in the
    IA32_MTRR_DEF_TYPE MSR to disable all MTRRs. All other bits in the
    MTRRs are undefined.

We currently do none of that, so whatever MTRR settings you had prior
to reset is what you have after reset.  Usually this doesn't matter
because KVM often ignores the guest mappings and uses write-back
anyway.  However, if you have an assigned device and an IOMMU that
allows NoSnoop for that device, KVM defers to the guest memory
mappings which are now stale after reset.  The result is that OVMF
rebooting on such a configuration takes a full minute to LZMA
decompress the firmware volume, a process that is nearly instant on
the initial boot.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 target-i386/cpu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 1507530..b76719d 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2398,6 +2398,16 @@ static void x86_cpu_reset(CPUState *s)
     cpu_breakpoint_remove_all(env, BP_CPU);
     cpu_watchpoint_remove_all(env, BP_CPU);
 
+    /*
+     * SDM 11.11.5 requires:
+     *  - IA32_MTRR_DEF_TYPE MSR.E = 0
+     *  - IA32_MTRR_PHYSMASKn.V = 0
+     * All other bits are undefined.  For simplification, zero it all.
+     */
+    env->mtrr_deftype = 0;
+    memset(env->mtrr_var, 0, sizeof(env->mtrr_var));
+    memset(env->mtrr_fixed, 0, sizeof(env->mtrr_fixed));
+
 #if !defined(CONFIG_USER_ONLY)
     /* We hard-wire the BSP to the first CPU. */
     if (s->cpu_index == 0) {
-- 
1.8.3.1