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From c48019a17552791a63cc143321944ed916de0672 Mon Sep 17 00:00:00 2001
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From: Eduardo Habkost <ehabkost@redhat.com>
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Date: Thu, 9 May 2019 22:43:18 +0100
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Subject: [PATCH 2/2] i386: kvm: Disable arch_capabilities if MSR can't be set
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RH-Author: Eduardo Habkost <ehabkost@redhat.com>
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Message-id: <20190509224318.23376-3-ehabkost@redhat.com>
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Patchwork-id: 87252
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O-Subject: [RHEL-8.1.0 qemu-kvm PATCH 2/2] i386: kvm: Disable arch_capabilities if MSR can't be set
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Bugzilla: 1707706
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
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RH-Acked-by: Bandan Das <bsd@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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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: Eduardo Habkost <ehabkost@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@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 e3e8c78..8a4d31d 100644
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--- a/target/i386/kvm.c
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+++ b/target/i386/kvm.c
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@@ -374,6 +374,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
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         if (host_tsx_blacklisted()) {
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             ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE);
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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_ECX) {
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         /*
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          * It's safe to enable TOPOEXT even if it's not returned by
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-- 
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1.8.3.1
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