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| author | Paolo Bonzini <pbonzini@redhat.com> | 2024-12-19 07:43:20 -0500 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-12-22 12:06:01 -0500 |
| commit | 398b7b6cb9e046f137a188670da12f790492b56b (patch) | |
| tree | b89da5abe77acc44ab1a85aa11abcb2abe12f070 | |
| parent | 37d1d99b8806b24ffe4a2b453620df932994a5c0 (diff) | |
| download | lwn-398b7b6cb9e046f137a188670da12f790492b56b.tar.gz lwn-398b7b6cb9e046f137a188670da12f790492b56b.zip | |
KVM: x86: let it be known that ignore_msrs is a bad idea
When running KVM with ignore_msrs=1 and report_ignored_msrs=0, the user has
no clue that that the guest is being lied to. This may cause bug reports
such as https://gitlab.com/qemu-project/qemu/-/issues/2571, where enabling
a CPUID bit in QEMU caused Linux guests to try reading MSR_CU_DEF_ERR; and
being lied about the existence of MSR_CU_DEF_ERR caused the guest to assume
other things about the local APIC which were not true:
Sep 14 12:02:53 kernel: mce: [Firmware Bug]: Your BIOS is not setting up LVT offset 0x2 for deferred error IRQs correctly.
Sep 14 12:02:53 kernel: unchecked MSR access error: RDMSR from 0x852 at rIP: 0xffffffffb548ffa7 (native_read_msr+0x7/0x40)
Sep 14 12:02:53 kernel: Call Trace:
...
Sep 14 12:02:53 kernel: native_apic_msr_read+0x20/0x30
Sep 14 12:02:53 kernel: setup_APIC_eilvt+0x47/0x110
Sep 14 12:02:53 kernel: mce_amd_feature_init+0x485/0x4e0
...
Sep 14 12:02:53 kernel: [Firmware Bug]: cpu 0, try to use APIC520 (LVT offset 2) for vector 0xf4, but the register is already in use for vector 0x0 on this cpu
Without reported_ignored_msrs=0 at least the host kernel log will contain
enough information to avoid going on a wild goose chase. But if reports
about individual MSR accesses are being silenced too, at least complain
loudly the first time a VM is started.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | arch/x86/kvm/x86.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c8160baf3838..12fa68a06966 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12724,6 +12724,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) kvm_hv_init_vm(kvm); kvm_xen_init_vm(kvm); + if (ignore_msrs && !report_ignored_msrs) { + pr_warn_once("Running KVM with ignore_msrs=1 and report_ignored_msrs=0 is not a\n" + "a supported configuration. Lying to the guest about the existence of MSRs\n" + "may cause the guest operating system to hang or produce errors. If a guest\n" + "does not run without ignore_msrs=1, please report it to kvm@vger.kernel.org.\n"); + } + return 0; out_uninit_mmu: |