linux-kernel - Re: [PATCH 3/5] mmu: don't set the present bit unconditionally

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Date:	Wed, 29 Jun 2016 11:17:39 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org
Cc:	pbonzini@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] mmu: don't set the present bit unconditionally



On 06/28/2016 12:32 PM, Bandan Das wrote:
> To support execute only mappings on behalf of L1
> hypervisors, we teach set_spte() to honor L1's valid XWR
> bits. This is only if host supports EPT execute only. Reuse
> ACC_USER_MASK to signify if the L1 hypervisor has the R bit
> set
>
> Signed-off-by: Bandan Das <bsd@...hat.com>
> ---
>   arch/x86/kvm/mmu.c         | 9 +++++++--
>   arch/x86/kvm/paging_tmpl.h | 2 +-
>   arch/x86/kvm/vmx.c         | 2 +-
>   3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 875d4f7..ee2fb16 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2516,13 +2516,17 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>   		    gfn_t gfn, kvm_pfn_t pfn, bool speculative,
>   		    bool can_unsync, bool host_writable)
>   {
> -	u64 spte;
> +	u64 spte = 0;
>   	int ret = 0;
> +	struct kvm_mmu *context = &vcpu->arch.mmu;
> +	bool execonly = !(context->guest_rsvd_check.bad_mt_xwr &
> +			  (1ull << VMX_EPT_EXECUTABLE_MASK));

Could we introduce a new field, say execonly, to "struct kvm_mmu"?
That would make the code be more clearer.