KVM: arm64: Introduce pkvm_alloc_private_va_range()

pkvm_hyp_alloc_private_va_range() can be used to reserve private VA ranges
in the pKVM nVHE hypervisor. Allocations are aligned based on the order of
the requested size.

This will be used to implement stack guard pages for pKVM nVHE hypervisor
(in a subsequent patch in the series).

Credits to Quentin Perret <qperret@google.com> for the idea of moving
private VA allocation out of __pkvm_create_private_mapping()

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220420214317.3303360-3-kaleshsingh@google.com

1 files changed, 51 insertions, 27 deletions

diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index cdbe8e246418..96193cb31a39 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -37,36 +37,60 @@ static int __pkvm_create_mappings(unsigned long start, unsigned long size,
 	return err;
 }
 
-unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
-					    enum kvm_pgtable_prot prot)
+/**
+ * pkvm_alloc_private_va_range - Allocates a private VA range.
+ * @size:	The size of the VA range to reserve.
+ * @haddr:	The hypervisor virtual start address of the allocation.
+ *
+ * The private virtual address (VA) range is allocated above __io_map_base
+ * and aligned based on the order of @size.
+ *
+ * Return: 0 on success or negative error code on failure.
+ */
+int pkvm_alloc_private_va_range(size_t size, unsigned long *haddr)
 {
-	unsigned long addr;
-	int err;
+	unsigned long base, addr;
+	int ret = 0;
 
 	hyp_spin_lock(&pkvm_pgd_lock);
 
-	size = PAGE_ALIGN(size + offset_in_page(phys));
-	addr = __io_map_base;
-	__io_map_base += size;
+	/* Align the allocation based on the order of its size */
+	addr = ALIGN(__io_map_base, PAGE_SIZE << get_order(size));
 
-	/* Are we overflowing on the vmemmap ? */
-	if (__io_map_base > __hyp_vmemmap) {
-		__io_map_base -= size;
-		addr = (unsigned long)ERR_PTR(-ENOMEM);
-		goto out;
-	}
+	/* The allocated size is always a multiple of PAGE_SIZE */
+	base = addr + PAGE_ALIGN(size);
 
-	err = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, size, phys, prot);
-	if (err) {
-		addr = (unsigned long)ERR_PTR(err);
-		goto out;
+	/* Are we overflowing on the vmemmap ? */
+	if (!addr || base > __hyp_vmemmap)
+		ret = -ENOMEM;
+	else {
+		__io_map_base = base;
+		*haddr = addr;
 	}
 
-	addr = addr + offset_in_page(phys);
-out:
 	hyp_spin_unlock(&pkvm_pgd_lock);
 
-	return addr;
+	return ret;
+}
+
+int __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
+				  enum kvm_pgtable_prot prot,
+				  unsigned long *haddr)
+{
+	unsigned long addr;
+	int err;
+
+	size = PAGE_ALIGN(size + offset_in_page(phys));
+	err = pkvm_alloc_private_va_range(size, &addr);
+	if (err)
+		return err;
+
+	err = __pkvm_create_mappings(addr, size, phys, prot);
+	if (err)
+		return err;
+
+	*haddr = addr + offset_in_page(phys);
+	return err;
 }
 
 int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot)
@@ -146,7 +170,8 @@ int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot)
 int hyp_map_vectors(void)
 {
 	phys_addr_t phys;
-	void *bp_base;
+	unsigned long bp_base;
+	int ret;
 
 	if (!kvm_system_needs_idmapped_vectors()) {
 		__hyp_bp_vect_base = __bp_harden_hyp_vecs;
@@ -154,13 +179,12 @@ int hyp_map_vectors(void)
 	}
 
 	phys = __hyp_pa(__bp_harden_hyp_vecs);
-	bp_base = (void *)__pkvm_create_private_mapping(phys,
-							__BP_HARDEN_HYP_VECS_SZ,
-							PAGE_HYP_EXEC);
-	if (IS_ERR_OR_NULL(bp_base))
-		return PTR_ERR(bp_base);
+	ret = __pkvm_create_private_mapping(phys, __BP_HARDEN_HYP_VECS_SZ,
+					    PAGE_HYP_EXEC, &bp_base);
+	if (ret)
+		return ret;
 
-	__hyp_bp_vect_base = bp_base;
+	__hyp_bp_vect_base = (void *)bp_base;
 
 	return 0;
 }