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

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Message-ID: <87tv33cdw8.fsf@vitty.brq.redhat.com>
Date:   Thu, 05 Mar 2020 11:08:39 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly

linmiaohe <linmiaohe@...wei.com> writes:

> From: Miaohe Lin <linmiaohe@...wei.com>
>
> (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. 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);
>  
> @@ -2797,7 +2797,7 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
>  	flags = vmcs_readl(GUEST_RFLAGS);
>  	vmx->rmode.save_rflags = flags;
>  
> -	flags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
> +	flags |= ~RMODE_GUEST_OWNED_EFLAGS_BITS;
>  
>  	vmcs_writel(GUEST_RFLAGS, flags);
>  	vmcs_writel(GUEST_CR4, vmcs_readl(GUEST_CR4) | X86_CR4_VME);

Double negations are evil, let's define a macro for 'X86_EFLAGS_IOPL |
X86_EFLAGS_VM' instead (completely untested):

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4ee19fb35cde..d838f93bd6d2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -139,7 +139,8 @@ module_param_named(preemption_timer, enable_preemption_timer, bool, S_IRUGO);
 #define KVM_PMODE_VM_CR4_ALWAYS_ON (X86_CR4_PAE | X86_CR4_VMXE)
 #define KVM_RMODE_VM_CR4_ALWAYS_ON (X86_CR4_VME | X86_CR4_PAE | X86_CR4_VMXE)
 
-#define RMODE_GUEST_OWNED_EFLAGS_BITS (~(X86_EFLAGS_IOPL | X86_EFLAGS_VM))
+#define RMODE_HOST_OWNED_EFLAGS_BITS (X86_EFLAGS_IOPL | X86_EFLAGS_VM)
+#define RMODE_GUEST_OWNED_EFLAGS_BITS (~RMODE_HOST_OWNED_EFLAGS_BITS)
 
 #define MSR_IA32_RTIT_STATUS_MASK (~(RTIT_STATUS_FILTEREN | \
        RTIT_STATUS_CONTEXTEN | RTIT_STATUS_TRIGGEREN | \
@@ -1468,7 +1469,7 @@ 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_HOST_OWNED_EFLAGS_BITS;
        }
        vmcs_writel(GUEST_RFLAGS, rflags);
 
@@ -2794,7 +2795,7 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
        flags = vmcs_readl(GUEST_RFLAGS);
        vmx->rmode.save_rflags = flags;
 
-       flags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
+       flags |= RMODE_HOST_OWNED_EFLAGS_BITS;
 
        vmcs_writel(GUEST_RFLAGS, flags);
        vmcs_writel(GUEST_CR4, vmcs_readl(GUEST_CR4) | X86_CR4_VME);

-- 
Vitaly