kvm: mmu: don't set the present bit unconditionally

To support execute only mappings on behalf of L1
hypervisors, we need to teach set_spte() to honor all three of
L1's XWR bits.  As a start, add a new variable "shadow_present_mask"
that will be set for non-EPT shadow paging and clear for EPT.

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7a628fb..d0845b2 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1031,7 +1031,7 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu);
 void kvm_mmu_init_vm(struct kvm *kvm);
 void kvm_mmu_uninit_vm(struct kvm *kvm);
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
-               u64 dirty_mask, u64 nx_mask, u64 x_mask);
+               u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask);
 
 void kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm,

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 6471f87..b8628e9 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -175,6 +175,7 @@ static u64 __read_mostly shadow_user_mask;
 static u64 __read_mostly shadow_accessed_mask;
 static u64 __read_mostly shadow_dirty_mask;
 static u64 __read_mostly shadow_mmio_mask;
+static u64 __read_mostly shadow_present_mask;
 
 static void mmu_spte_set(u64 *sptep, u64 spte);
 static void mmu_free_roots(struct kvm_vcpu *vcpu);
@@ -282,13 +283,14 @@ static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
 }
 
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
-               u64 dirty_mask, u64 nx_mask, u64 x_mask)
+               u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask)
 {
        shadow_user_mask = user_mask;
        shadow_accessed_mask = accessed_mask;
        shadow_dirty_mask = dirty_mask;
        shadow_nx_mask = nx_mask;
        shadow_x_mask = x_mask;
+       shadow_present_mask = p_mask;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
 
@@ -2245,10 +2247,9 @@ static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
 {
        u64 spte;
 
-       BUILD_BUG_ON(VMX_EPT_READABLE_MASK != PT_PRESENT_MASK ||
-                       VMX_EPT_WRITABLE_MASK != PT_WRITABLE_MASK);
+       BUILD_BUG_ON(VMX_EPT_WRITABLE_MASK != PT_WRITABLE_MASK);
 
-       spte = __pa(sp->spt) | PT_PRESENT_MASK | PT_WRITABLE_MASK |
+       spte = __pa(sp->spt) | shadow_present_mask | PT_WRITABLE_MASK |
               shadow_user_mask | shadow_x_mask | shadow_accessed_mask;
 
        mmu_spte_set(sptep, spte);
@@ -2515,13 +2516,13 @@ 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;
 
        if (set_mmio_spte(vcpu, sptep, gfn, pfn, pte_access))
                return 0;
 
-       spte = PT_PRESENT_MASK;
+       spte |= shadow_present_mask;
        if (!speculative)
                spte |= shadow_accessed_mask;
 

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e515030..a75d09d 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6473,6 +6473,7 @@ static __init int hardware_setup(void)
                        (enable_ept_ad_bits) ? VMX_EPT_ACCESS_BIT : 0ull,
                        (enable_ept_ad_bits) ? VMX_EPT_DIRTY_BIT : 0ull,
                        0ull, VMX_EPT_EXECUTABLE_MASK);
+                       0ull, VMX_EPT_EXECUTABLE_MASK, VMX_EPT_READABLE_MASK);
                ept_set_mmio_spte_mask();
                kvm_enable_tdp();
        } else

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bb6e8bf..0c1fbb8 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5878,8 +5878,8 @@ int kvm_arch_init(void *opaque)
        kvm_x86_ops = ops;
 
        kvm_mmu_set_mask_ptes(PT_USER_MASK, PT_ACCESSED_MASK,
-                       PT_DIRTY_MASK, PT64_NX_MASK, 0);
-
+                       PT_DIRTY_MASK, PT64_NX_MASK, 0,
+                       PT_PRESENT_MASK);
        kvm_timer_init();
 
        perf_register_guest_info_callbacks(&kvm_guest_cbs);