linux-kernel - Re: [PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated CPUID bit

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Date:   Wed, 5 Feb 2020 16:30:32 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated
 CPUID bit

On 29/01/20 00:53, Sean Christopherson wrote:
> Re-add code to mark CR4.UMIP as reserved if UMIP is not supported by the
> host.  The UMIP handling was unintentionally dropped during a recent
> refactoring.
> 
> Not flagging CR4.UMIP allows the guest to set its CR4.UMIP regardless of
> host support or userspace desires.  On CPUs with UMIP support, including
> emulated UMIP, this allows the guest to enable UMIP against the wishes
> of the userspace VMM.  On CPUs without any form of UMIP, this results in
> a failed VM-Enter due to invalid guest state.
> 
> Fixes: 345599f9a2928 ("KVM: x86: Add macro to ensure reserved cr4 bits checks stay in sync")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/x86.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7e3f1d937224..e70d1215638a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -898,6 +898,8 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
>  		__reserved_bits |= X86_CR4_PKE;		\
>  	if (!__cpu_has(__c, X86_FEATURE_LA57))		\
>  		__reserved_bits |= X86_CR4_LA57;	\
> +	if (!__cpu_has(__c, X86_FEATURE_UMIP))		\
> +		__reserved_bits |= X86_CR4_UMIP;	\
>  	__reserved_bits;				\
>  })
>  
> 

Queued, thanks.

Paolo