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

Xiao Guangrong
2016-06-29T03:21:34Z

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@redhat.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.