KVM: propagate fault r/w information to gup(), allow read-only memory

As suggested by Andrea, pass r/w error code to gup(), upgrading read fault
to writable if host pte allows it.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 26 insertions, 14 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 99433943170..53509f5973d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2216,7 +2216,7 @@ static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep)
 }
 
 static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
-			int level, gfn_t gfn, pfn_t pfn)
+			int map_writable, int level, gfn_t gfn, pfn_t pfn)
 {
 	struct kvm_shadow_walk_iterator iterator;
 	struct kvm_mmu_page *sp;
@@ -2225,9 +2225,13 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 
 	for_each_shadow_entry(vcpu, (u64)gfn << PAGE_SHIFT, iterator) {
 		if (iterator.level == level) {
-			mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, ACC_ALL,
+			unsigned pte_access = ACC_ALL;
+
+			if (!map_writable)
+				pte_access &= ~ACC_WRITE_MASK;
+			mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, pte_access,
 				     0, write, 1, &pt_write,
-				     level, gfn, pfn, false, true);
+				     level, gfn, pfn, false, map_writable);
 			direct_pte_prefetch(vcpu, iterator.sptep);
 			++vcpu->stat.pf_fixed;
 			break;
@@ -2288,6 +2292,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
 	int level;
 	pfn_t pfn;
 	unsigned long mmu_seq;
+	bool map_writable;
 
 	level = mapping_level(vcpu, gfn);
 
@@ -2302,7 +2307,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
-	pfn = gfn_to_pfn(vcpu->kvm, gfn);
+	pfn = gfn_to_pfn_prot(vcpu->kvm, gfn, write, &map_writable);
 
 	/* mmio */
 	if (is_error_pfn(pfn))
@@ -2312,7 +2317,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
 	if (mmu_notifier_retry(vcpu, mmu_seq))
 		goto out_unlock;
 	kvm_mmu_free_some_pages(vcpu);
-	r = __direct_map(vcpu, v, write, level, gfn, pfn);
+	r = __direct_map(vcpu, v, write, map_writable, level, gfn, pfn);
 	spin_unlock(&vcpu->kvm->mmu_lock);
 
 
@@ -2611,11 +2616,11 @@ static bool can_do_async_pf(struct kvm_vcpu *vcpu)
 }
 
 static bool try_async_pf(struct kvm_vcpu *vcpu, bool no_apf, gfn_t gfn,
-			 gva_t gva, pfn_t *pfn)
+			 gva_t gva, pfn_t *pfn, bool write, bool *writable)
 {
 	bool async;
 
-	*pfn = gfn_to_pfn_async(vcpu->kvm, gfn, &async);
+	*pfn = gfn_to_pfn_async(vcpu->kvm, gfn, &async, write, writable);
 
 	if (!async)
 		return false; /* *pfn has correct page already */
@@ -2632,7 +2637,7 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool no_apf, gfn_t gfn,
 			return true;
 	}
 
-	*pfn = gfn_to_pfn(vcpu->kvm, gfn);
+	*pfn = gfn_to_pfn_prot(vcpu->kvm, gfn, write, writable);
 
 	return false;
 }
@@ -2645,6 +2650,8 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 	int level;
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	unsigned long mmu_seq;
+	int write = error_code & PFERR_WRITE_MASK;
+	bool map_writable;
 
 	ASSERT(vcpu);
 	ASSERT(VALID_PAGE(vcpu->arch.mmu.root_hpa));
@@ -2660,7 +2667,7 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
 
-	if (try_async_pf(vcpu, no_apf, gfn, gpa, &pfn))
+	if (try_async_pf(vcpu, no_apf, gfn, gpa, &pfn, write, &map_writable))
 		return 0;
 
 	/* mmio */
@@ -2670,7 +2677,7 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 	if (mmu_notifier_retry(vcpu, mmu_seq))
 		goto out_unlock;
 	kvm_mmu_free_some_pages(vcpu);
-	r = __direct_map(vcpu, gpa, error_code & PFERR_WRITE_MASK,
+	r = __direct_map(vcpu, gpa, write, map_writable,
 			 level, gfn, pfn);
 	spin_unlock(&vcpu->kvm->mmu_lock);
 
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index d6b281e989b..ba00eefa7bc 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -427,7 +427,7 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
 static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 			 struct guest_walker *gw,
 			 int user_fault, int write_fault, int hlevel,
-			 int *ptwrite, pfn_t pfn)
+			 int *ptwrite, pfn_t pfn, bool map_writable)
 {
 	unsigned access = gw->pt_access;
 	struct kvm_mmu_page *sp = NULL;
@@ -501,7 +501,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 
 	mmu_set_spte(vcpu, it.sptep, access, gw->pte_access & access,
 		     user_fault, write_fault, dirty, ptwrite, it.level,
-		     gw->gfn, pfn, false, true);
+		     gw->gfn, pfn, false, map_writable);
 	FNAME(pte_prefetch)(vcpu, gw, it.sptep);
 
 	return it.sptep;
@@ -539,6 +539,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 	pfn_t pfn;
 	int level = PT_PAGE_TABLE_LEVEL;
 	unsigned long mmu_seq;
+	bool map_writable;
 
 	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
 
@@ -569,13 +570,17 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
 
-	if (try_async_pf(vcpu, no_apf, walker.gfn, addr, &pfn))
+	if (try_async_pf(vcpu, no_apf, walker.gfn, addr, &pfn, write_fault,
+			 &map_writable))
 		return 0;
 
 	/* mmio */
 	if (is_error_pfn(pfn))
 		return kvm_handle_bad_page(vcpu->kvm, walker.gfn, pfn);
 
+	if (!map_writable)
+		walker.pte_access &= ~ACC_WRITE_MASK;
+
 	spin_lock(&vcpu->kvm->mmu_lock);
 	if (mmu_notifier_retry(vcpu, mmu_seq))
 		goto out_unlock;
@@ -583,7 +588,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 	trace_kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
 	kvm_mmu_free_some_pages(vcpu);
 	sptep = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
-			     level, &write_pt, pfn);
+			     level, &write_pt, pfn, map_writable);
 	(void)sptep;
 	pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __func__,
 		 sptep, *sptep, write_pt);