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From 2f6d988d14532616d1f1f476b438b4e3295329f1 Mon Sep 17 00:00:00 2001
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From: Alex Williamson <alex.williamson@redhat.com>
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Date: Fri, 10 Apr 2015 16:45:59 +0200
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Subject: [PATCH 13/14] x86: Clear MTRRs on vCPU reset
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Message-id: <20150410164559.16166.37319.stgit@gimli.home>
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Patchwork-id: 64799
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O-Subject: [RHEL7.2 qemu-kvm PATCH 3/3] x86: Clear MTRRs on vCPU reset
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Bugzilla: 1210510
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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Upstream: 9db2efd95e13330075bff027cd682a063d725332
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The SDM specifies (June 2014 Vol3 11.11.5):
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On a hardware reset, the P6 and more recent processors clear the
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valid flags in variable-range MTRRs and clear the E flag in the
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IA32_MTRR_DEF_TYPE MSR to disable all MTRRs. All other bits in the
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MTRRs are undefined.
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We currently do none of that, so whatever MTRR settings you had prior
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to reset is what you have after reset. Usually this doesn't matter
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because KVM often ignores the guest mappings and uses write-back
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anyway. However, if you have an assigned device and an IOMMU that
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allows NoSnoop for that device, KVM defers to the guest memory
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mappings which are now stale after reset. The result is that OVMF
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rebooting on such a configuration takes a full minute to LZMA
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decompress the firmware volume, a process that is nearly instant on
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the initial boot.
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Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Reviewed-by: Laszlo Ersek <lersek@redhat.com>
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Cc: qemu-stable@nongnu.org
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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target-i386/cpu.c | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/target-i386/cpu.c b/target-i386/cpu.c
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index 1507530..b76719d 100644
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--- a/target-i386/cpu.c
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+++ b/target-i386/cpu.c
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@@ -2398,6 +2398,16 @@ static void x86_cpu_reset(CPUState *s)
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cpu_breakpoint_remove_all(env, BP_CPU);
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cpu_watchpoint_remove_all(env, BP_CPU);
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+ /*
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+ * SDM 11.11.5 requires:
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+ * - IA32_MTRR_DEF_TYPE MSR.E = 0
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+ * - IA32_MTRR_PHYSMASKn.V = 0
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+ * All other bits are undefined. For simplification, zero it all.
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+ */
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+ env->mtrr_deftype = 0;
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+ memset(env->mtrr_var, 0, sizeof(env->mtrr_var));
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+ memset(env->mtrr_fixed, 0, sizeof(env->mtrr_fixed));
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+
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#if !defined(CONFIG_USER_ONLY)
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/* We hard-wire the BSP to the first CPU. */
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if (s->cpu_index == 0) {
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--
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1.8.3.1
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