From: Sean Christopherson seanjc@google.com
commit 31de69f4eea77b28a9724b3fa55aae104fc91fc7 upstream.
Set ENABLE_USR_WAIT_PAUSE in KVM's supported VMX MSR configuration if the feature is supported in hardware and enabled in KVM's base, non-nested configuration, i.e. expose ENABLE_USR_WAIT_PAUSE to L1 if it's supported. This fixes a bug where saving/restoring, i.e. migrating, a vCPU will fail if WAITPKG (the associated CPUID feature) is enabled for the vCPU, and obviously allows L1 to enable the feature for L2.
KVM already effectively exposes ENABLE_USR_WAIT_PAUSE to L1 by stuffing the allowed-1 control ina vCPU's virtual MSR_IA32_VMX_PROCBASED_CTLS2 when updating secondary controls in response to KVM_SET_CPUID(2), but (a) that depends on flawed code (KVM shouldn't touch VMX MSRs in response to CPUID updates) and (b) runs afoul of vmx_restore_control_msr()'s restriction that the guest value must be a strict subset of the supported host value.
Although no past commit explicitly enabled nested support for WAITPKG, doing so is safe and functionally correct from an architectural perspective as no additional KVM support is needed to virtualize TPAUSE, UMONITOR, and UMWAIT for L2 relative to L1, and KVM already forwards VM-Exits to L1 as necessary (commit bf653b78f960, "KVM: vmx: Introduce handle_unexpected_vmexit and handle WAITPKG vmexit").
Note, KVM always keeps the hosts MSR_IA32_UMWAIT_CONTROL resident in hardware, i.e. always runs both L1 and L2 with the host's power management settings for TPAUSE and UMWAIT. See commit bf09fb6cba4f ("KVM: VMX: Stop context switching MSR_IA32_UMWAIT_CONTROL") for more details.
Fixes: e69e72faa3a0 ("KVM: x86: Add support for user wait instructions") Cc: stable@vger.kernel.org Reported-by: Aaron Lewis aaronlewis@google.com Reported-by: Yu Zhang yu.c.zhang@linux.intel.com Signed-off-by: Sean Christopherson seanjc@google.com Reviewed-by: Jim Mattson jmattson@google.com Message-Id: 20221213062306.667649-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/vmx/nested.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -6666,7 +6666,8 @@ void nested_vmx_setup_ctls_msrs(struct n SECONDARY_EXEC_ENABLE_INVPCID | SECONDARY_EXEC_RDSEED_EXITING | SECONDARY_EXEC_XSAVES | - SECONDARY_EXEC_TSC_SCALING; + SECONDARY_EXEC_TSC_SCALING | + SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
/* * We can emulate "VMCS shadowing," even if the hardware