linux-kernel - Re: [PATCH 2/5] mmu: pass execonly value when initializing rsvd bits

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Date:	Wed, 29 Jun 2016 11:07:56 +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 2/5] mmu: pass execonly value when initializing rsvd bits



On 06/28/2016 12:32 PM, Bandan Das wrote:
> In reset_tdp_shadow_zero_bits_mask, we always pass false
> when initializing the reserved bits. By initializing with the
> correct value of ept exec only, the host can correctly
> identify if the guest pte is valid. Note that
> kvm_init_shadow_ept_mmu() already knows about execonly.
>
> Signed-off-by: Bandan Das <bsd@...hat.com>
> ---
>   arch/x86/kvm/mmu.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index a50af79..875d4f7 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3831,23 +3831,27 @@ static inline bool boot_cpu_is_amd(void)
>
>   /*
>    * the direct page table on host, use as much mmu features as
> - * possible, however, kvm currently does not do execution-protection.
> + * possible
>    */
>   static void
>   reset_tdp_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,
>   				struct kvm_mmu *context)
>   {

It is not necessary. reset_tdp_shadow_zero_bits_mask() is used for
the guest without nested-ept, host never sets shadow execute-only
actively.

For the nested ept guest, kvm_init_shadow_ept_mmu() has already
handled xonly case perfectly.