[PATCH v2 24/30] KVM: arm64: Restrict the scope of the 'writable' attribute

[Marc Zyngier]

The 'writable' field is ambiguous, and indicates multiple things:

- whether the underlying memslot is writable

- whether we are resolving the fault with writable attributes

Add a new field to kvm_s2_fault_vma_info (map_writable) to indicate
the former condition, and have local writable variables to track
the latter.

Tested-by: Fuad Tabba <tabba at google.com>
Reviewed-by: Fuad Tabba <tabba at google.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/mmu.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 26313e0b40c25..91767a2e6e9f2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1655,6 +1655,7 @@ struct kvm_s2_fault_vma_info {
 	gfn_t		gfn;
 	bool		mte_allowed;
 	bool		is_vma_cacheable;
+	bool		map_writable;
 };
 
 static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
@@ -1720,7 +1721,6 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
 }
 
 struct kvm_s2_fault {
-	bool writable;
 	bool s2_force_noncacheable;
 	kvm_pfn_t pfn;
 	bool force_pte;
@@ -1801,7 +1801,7 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
 
 	fault->pfn = __kvm_faultin_pfn(s2fd->memslot, get_canonical_gfn(s2fd, s2vi),
 				       kvm_is_write_fault(s2fd->vcpu) ? FOLL_WRITE : 0,
-				       &fault->writable, &fault->page);
+				       &s2vi->map_writable, &fault->page);
 	if (unlikely(is_error_noslot_pfn(fault->pfn))) {
 		if (fault->pfn == KVM_PFN_ERR_HWPOISON) {
 			kvm_send_hwpoison_signal(s2fd->hva, __ffs(s2vi->vma_pagesize));
@@ -1818,6 +1818,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 				     const struct kvm_s2_fault_vma_info *s2vi)
 {
 	struct kvm *kvm = s2fd->vcpu->kvm;
+	bool writable = s2vi->map_writable;
 
 	/*
 	 * Check if this is non-struct page memory PFN, and cannot support
@@ -1857,7 +1858,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 		 * Only actually map the page as writable if this was a write
 		 * fault.
 		 */
-		fault->writable = false;
+		writable = false;
 	}
 
 	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && fault->s2_force_noncacheable)
@@ -1875,9 +1876,9 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 	}
 
 	if (s2fd->nested)
-		adjust_nested_fault_perms(s2fd->nested, &fault->prot, &fault->writable);
+		adjust_nested_fault_perms(s2fd->nested, &fault->prot, &writable);
 
-	if (fault->writable)
+	if (writable)
 		fault->prot |= KVM_PGTABLE_PROT_W;
 
 	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu))
@@ -1906,6 +1907,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 			    const struct kvm_s2_fault_vma_info *s2vi, void *memcache)
 {
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
+	bool writable = fault->prot & KVM_PGTABLE_PROT_W;
 	struct kvm *kvm = s2fd->vcpu->kvm;
 	struct kvm_pgtable *pgt;
 	long perm_fault_granule;
@@ -1966,7 +1968,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 	}
 
 out_unlock:
-	kvm_release_faultin_page(kvm, fault->page, !!ret, fault->writable);
+	kvm_release_faultin_page(kvm, fault->page, !!ret, writable);
 	kvm_fault_unlock(kvm);
 
 	/*
@@ -1974,7 +1976,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 	 * making sure we adjust the canonical IPA if the mapping size has
 	 * been updated (via a THP upgrade, for example).
 	 */
-	if (fault->writable && !ret) {
+	if (writable && !ret) {
 		phys_addr_t ipa = gfn_to_gpa(get_canonical_gfn(s2fd, s2vi));
 		ipa &= ~(mapping_size - 1);
 		mark_page_dirty_in_slot(kvm, s2fd->memslot, gpa_to_gfn(ipa));
-- 
2.47.3