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From e9ae571d86a83652aa43f9b866f619709b1feda2 Mon Sep 17 00:00:00 2001
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From: Eduardo Habkost <ehabkost@redhat.com>
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Date: Wed, 9 Oct 2019 17:51:47 +0200
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Subject: [PATCH 09/10] i386: kvm: Disable arch_capabilities if MSR can't be
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set
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RH-Author: Eduardo Habkost <ehabkost@redhat.com>
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Message-id: <20191009175148.1361-10-ehabkost@redhat.com>
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Patchwork-id: 91365
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O-Subject: [RHEL-7.7.z qemu-kvm PATCH 09/10] i386: kvm: Disable arch_capabilities if MSR can't be set
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Bugzilla: 1730606
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Bandan Das <bsd@redhat.com>
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RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
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KVM has two bugs in the handling of MSR_IA32_ARCH_CAPABILITIES:
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1) Linux commit commit 1eaafe91a0df ("kvm: x86: IA32_ARCH_CAPABILITIES
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is always supported") makes GET_SUPPORTED_CPUID return
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arch_capabilities even if running on SVM. This makes "-cpu
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host,migratable=off" incorrectly expose arch_capabilities on CPUID on
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AMD hosts (where the MSR is not emulated by KVM).
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2) KVM_GET_MSR_INDEX_LIST does not return MSR_IA32_ARCH_CAPABILITIES if
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the MSR is not supported by the host CPU. This makes QEMU not
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initialize the MSR properly at kvm_put_msrs() on those hosts.
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Work around both bugs on the QEMU side, by checking if the MSR
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was returned by KVM_GET_MSR_INDEX_LIST before returning the
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feature flag on kvm_arch_get_supported_cpuid().
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This has the unfortunate side effect of making arch_capabilities
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unavailable on hosts without hardware support for the MSR until bug #2
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is fixed on KVM, but I can't see another way to work around bug #1
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without that side effect.
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7.8 backport conflicts (plai):
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target/i386/kvm.c changes to target-i386/kvm.c
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7.7.z backport notes (ehabkost):
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* Cherry pick from 7.8 tree with no conflicts
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Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
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Message-Id: <20190125220606.4864-2-ehabkost@redhat.com>
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Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
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(cherry picked from commit 485b1d256bcb0874bcde0223727c159b6837e6f8)
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Signed-off-by: Paul Lai <plai@redhat.com>
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Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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target-i386/kvm.c | 9 +++++++++
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1 file changed, 9 insertions(+)
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diff --git a/target-i386/kvm.c b/target-i386/kvm.c
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index bc3a514..0374b7a 100644
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--- a/target-i386/kvm.c
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+++ b/target-i386/kvm.c
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@@ -234,6 +234,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
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if (!kvm_irqchip_in_kernel()) {
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ret &= ~CPUID_EXT_X2APIC;
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}
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+ } else if (function == 7 && index == 0 && reg == R_EDX) {
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+ /*
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+ * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts.
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+ * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is
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+ * returned by KVM_GET_MSR_INDEX_LIST.
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+ */
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+ if (!has_msr_arch_capabs) {
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+ ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES;
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+ }
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} else if (function == 0x80000001 && reg == R_EDX) {
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/* On Intel, kvm returns cpuid according to the Intel spec,
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* so add missing bits according to the AMD spec:
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--
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1.8.3.1
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