| From 178a63f8515a461a6625b856d25f4d4154ada960 Mon Sep 17 00:00:00 2001 |
| From: "plai@redhat.com" <plai@redhat.com> |
| Date: Mon, 23 Sep 2019 20:40:26 +0200 |
| Subject: [PATCH 10/12] i386: kvm: Disable arch_capabilities if MSR can't be |
| set |
| |
| RH-Author: plai@redhat.com |
| Message-id: <1569271227-28026-10-git-send-email-plai@redhat.com> |
| Patchwork-id: 90858 |
| O-Subject: [RHEL7.8 qemu-kvm PATCH v6 09/10] i386: kvm: Disable arch_capabilities if MSR can't be set |
| Bugzilla: 1709971 |
| RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com> |
| RH-Acked-by: Bandan Das <bsd@redhat.com> |
| RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com> |
| |
| From: Eduardo Habkost <ehabkost@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: Paul Lai <plai@redhat.com> |
| Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com> |
| |
| Conflicts: |
| target/i386/kvm.c changes to target-i386/kvm.c |
| |
| target-i386/kvm.c | 9 +++++++++ |
| 1 file changed, 9 insertions(+) |
| |
| diff --git a/target-i386/kvm.c b/target-i386/kvm.c |
| index 12781a8..c79b0ea 100644 |
| |
| |
| @@ -235,6 +235,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function, |
| if (!kvm_irqchip_in_kernel()) { |
| ret &= ~CPUID_EXT_X2APIC; |
| } |
| + } 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_EDX) { |
| /* On Intel, kvm returns cpuid according to the Intel spec, |
| * so add missing bits according to the AMD spec: |
| -- |
| 1.8.3.1 |
| |