From c48019a17552791a63cc143321944ed916de0672 Mon Sep 17 00:00:00 2001

From: Eduardo Habkost <ehabkost@redhat.com>

Date: Thu, 9 May 2019 22:43:18 +0100

Subject: [PATCH 2/2] i386: kvm: Disable arch_capabilities if MSR can't be set

RH-Author: Eduardo Habkost <ehabkost@redhat.com>

Message-id: <20190509224318.23376-3-ehabkost@redhat.com>

Patchwork-id: 87252

O-Subject: [RHEL-8.1.0 qemu-kvm PATCH 2/2] i386: kvm: Disable arch_capabilities if MSR can't be set

Bugzilla: 1707706

RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

RH-Acked-by: Igor Mammedov <imammedo@redhat.com>

RH-Acked-by: Bandan Das <bsd@redhat.com>

KVM has two bugs in the handling of MSR_IA32_ARCH_CAPABILITIES:

1) Linux commit commit 1eaafe91a0df ("kvm: x86: IA32_ARCH_CAPABILITIES

   is always supported") makes GET_SUPPORTED_CPUID return

   arch_capabilities even if running on SVM.  This makes "-cpu

   host,migratable=off" incorrectly expose arch_capabilities on CPUID on

   AMD hosts (where the MSR is not emulated by KVM).

2) KVM_GET_MSR_INDEX_LIST does not return MSR_IA32_ARCH_CAPABILITIES if

   the MSR is not supported by the host CPU.  This makes QEMU not

   initialize the MSR properly at kvm_put_msrs() on those hosts.

Work around both bugs on the QEMU side, by checking if the MSR

was returned by KVM_GET_MSR_INDEX_LIST before returning the

feature flag on kvm_arch_get_supported_cpuid().

This has the unfortunate side effect of making arch_capabilities

unavailable on hosts without hardware support for the MSR until bug #2

is fixed on KVM, but I can't see another way to work around bug #1

without that side effect.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Message-Id: <20190125220606.4864-2-ehabkost@redhat.com>

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

(cherry picked from commit 485b1d256bcb0874bcde0223727c159b6837e6f8)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 target/i386/kvm.c | 9 +++++++++

 1 file changed, 9 insertions(+)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c

index e3e8c78..8a4d31d 100644

--- a/target/i386/kvm.c

+++ b/target/i386/kvm.c

@@ -374,6 +374,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,

         if (host_tsx_blacklisted()) {

             ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE);

         }

+    } else if (function == 7 && index == 0 && reg == R_EDX) {

+        /*

+         * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts.

+         * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is

+         * returned by KVM_GET_MSR_INDEX_LIST.

+         */

+        if (!has_msr_arch_capabs) {

+            ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES;

+        }

     } else if (function == 0x80000001 && reg == R_ECX) {

         /*

          * It's safe to enable TOPOEXT even if it's not returned by

-- 

1.8.3.1