ACK: [SRU Bionic 1/1] KVM: nVMX: Always reflect #NM VM-exits to L1

[Stefan Bader]

On 03.12.20 21:33, Thadeu Lima de Souza Cascardo wrote:
> From: Jim Mattson <jmattson at google.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1872401
> 
> When bit 3 (corresponding to CR0.TS) of the VMCS12 cr0_guest_host_mask
> field is clear, the VMCS12 guest_cr0 field does not necessarily hold
> the current value of the L2 CR0.TS bit, so the code that checked for
> L2's CR0.TS bit being set was incorrect. Moreover, I'm not sure that
> the CR0.TS check was adequate. (What if L2's CR0.EM was set, for
> instance?)
> 
> Fortunately, lazy FPU has gone away, so L0 has lost all interest in
> intercepting #NM exceptions. See commit bd7e5b0899a4 ("KVM: x86:
> remove code for lazy FPU handling"). Therefore, there is no longer any
> question of which hypervisor gets first dibs. The #NM VM-exit should
> always be reflected to L1. (Note that the corresponding bit must be
> set in the VMCS12 exception_bitmap field for there to be an #NM
> VM-exit at all.)
> 
> Fixes: ccf9844e5d99c ("kvm, vmx: Really fix lazy FPU on nested guest")
> Reported-by: Abhiroop Dabral <adabral at paloaltonetworks.com>
> Signed-off-by: Jim Mattson <jmattson at google.com>
> Reviewed-by: Peter Shier <pshier at google.com>
> Tested-by: Abhiroop Dabral <adabral at paloaltonetworks.com>
> Reviewed-by: Liran Alon <liran.alon at oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
> (cherry picked from commit 3c6e099fa15fdb6fb1892199ed8709012e1294f2)
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  arch/x86/kvm/vmx.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index dd940ac9cf88..2773499f3578 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1215,11 +1215,6 @@ static inline bool is_page_fault(u32 intr_info)
>  	return is_exception_n(intr_info, PF_VECTOR);
>  }
>  
> -static inline bool is_no_device(u32 intr_info)
> -{
> -	return is_exception_n(intr_info, NM_VECTOR);
> -}
> -
>  static inline bool is_invalid_opcode(u32 intr_info)
>  {
>  	return is_exception_n(intr_info, UD_VECTOR);
> @@ -8726,9 +8721,6 @@ static bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
>  			return false;
>  		else if (is_page_fault(intr_info))
>  			return !vmx->vcpu.arch.apf.host_apf_reason && enable_ept;
> -		else if (is_no_device(intr_info) &&
> -			 !(vmcs12->guest_cr0 & X86_CR0_TS))
> -			return false;
>  		else if (is_debug(intr_info) &&
>  			 vcpu->guest_debug &
>  			 (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
> 


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