linux-kernel - Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS

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Date:   Thu, 5 Mar 2020 12:49:23 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, vkuznets@...hat.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] KVM: VMX: Use wrapper macro
 ~RMODE_GUEST_OWNED_EFLAGS_BITS directly

On 05/03/20 03:35, linmiaohe wrote:
> (X86_EFLAGS_IOPL | X86_EFLAGS_VM) indicates the eflag bits that can not be
> owned by realmode guest, i.e. ~RMODE_GUEST_OWNED_EFLAGS_BITS.

... but ~RMODE_GUEST_OWNED_EFLAGS_BITS is the bits that are owned by the
host; they could be 0 or 1 and that's why the code was using
X86_EFLAGS_IOPL | X86_EFLAGS_VM.

I understand where ~RMODE_GUEST_OWNED_EFLAGS_BITS is better than
X86_EFLAGS_IOPL | X86_EFLAGS_VM, but I cannot think of a way to express
it that is the best of both worlds.

Paolo

 Use wrapper
> macro directly to make it clear and also improve readability.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 743b81642ce2..9571f8dea016 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1466,7 +1466,7 @@ void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>  	vmx->rflags = rflags;
>  	if (vmx->rmode.vm86_active) {
>  		vmx->rmode.save_rflags = rflags;
> -		rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
> +		rflags |= ~RMODE_GUEST_OWNED_EFLAGS_BITS;
>  	}
>  	vmcs_writel(GUEST_RFLAGS, rflags);