[PATCH v2 2/9] KVM: arm64: Introduce pkvm_alloc_private_va_range()

[Kalesh Singh <kaleshsingh@google.com>]

pkvm_hyp_alloc_private_va_range() can be used to reserve private VA ranges
in the pKVM nVHE hypervisor (). Also update __pkvm_create_private_mapping()
to allow specifying an alignment for the private VA mapping.

These 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>
---

Changes in v2:
  - Allow specifying an alignment for the private VA allocations, per Marc

 arch/arm64/kvm/hyp/include/nvhe/mm.h |  3 +-
 arch/arm64/kvm/hyp/nvhe/hyp-main.c   |  5 +--
 arch/arm64/kvm/hyp/nvhe/mm.c         | 49 +++++++++++++++++++---------
 arch/arm64/kvm/mmu.c                 |  2 +-
 4 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
index 2d08510c6cc1..05d06ad00347 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
@@ -20,7 +20,8 @@ int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
 int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
 int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot);
 unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
-					    enum kvm_pgtable_prot prot);
+					size_t align, enum kvm_pgtable_prot prot);
+unsigned long pkvm_alloc_private_va_range(size_t size, size_t align);
 
 static inline void hyp_vmemmap_range(phys_addr_t phys, unsigned long size,
 				     unsigned long *start, unsigned long *end)
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 5e2197db0d32..96b2312a0f1d 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -158,9 +158,10 @@ static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ct
 {
 	DECLARE_REG(phys_addr_t, phys, host_ctxt, 1);
 	DECLARE_REG(size_t, size, host_ctxt, 2);
-	DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 3);
+	DECLARE_REG(size_t, align, host_ctxt, 3);
+	DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4);
 
-	cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, prot);
+	cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, align, prot);
 }
 
 static void handle___pkvm_prot_finalize(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index 526a7d6fa86f..298fbbe4651d 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -37,26 +37,46 @@ 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)
+/*
+ * Allocates a private VA range above __io_map_base.
+ *
+ * @size:	The size of the VA range to reserve.
+ * @align:	The required alignment for the allocation.
+ */
+unsigned long pkvm_alloc_private_va_range(size_t size, size_t align)
 {
-	unsigned long addr;
-	int err;
+	unsigned long base, addr;
 
 	hyp_spin_lock(&pkvm_pgd_lock);
 
-	size = PAGE_ALIGN(size + offset_in_page(phys));
-	addr = __io_map_base;
-	__io_map_base += size;
+	addr = ALIGN(__io_map_base, align);
+
+	/* The allocated size is always a multiple of PAGE_SIZE */
+	base = addr + PAGE_ALIGN(size);
 
 	/* Are we overflowing on the vmemmap ? */
-	if (__io_map_base > __hyp_vmemmap) {
-		__io_map_base -= size;
+	if (base > __hyp_vmemmap)
 		addr = (unsigned long)ERR_PTR(-ENOMEM);
+	else
+		__io_map_base = base;
+
+	hyp_spin_unlock(&pkvm_pgd_lock);
+
+	return addr;
+}
+
+unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
+					size_t align, enum kvm_pgtable_prot prot)
+{
+	unsigned long addr;
+	int err;
+
+	size += offset_in_page(phys);
+	addr = pkvm_alloc_private_va_range(size, align);
+	if (IS_ERR((void *)addr))
 		goto out;
-	}
 
-	err = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, size, phys, prot);
+	err = __pkvm_create_mappings(addr, size, phys, prot);
 	if (err) {
 		addr = (unsigned long)ERR_PTR(err);
 		goto out;
@@ -64,8 +84,6 @@ unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
 
 	addr = addr + offset_in_page(phys);
 out:
-	hyp_spin_unlock(&pkvm_pgd_lock);
-
 	return addr;
 }
 
@@ -152,9 +170,8 @@ int hyp_map_vectors(void)
 		return 0;
 
 	phys = __hyp_pa(__bp_harden_hyp_vecs);
-	bp_base = (void *)__pkvm_create_private_mapping(phys,
-							__BP_HARDEN_HYP_VECS_SZ,
-							PAGE_HYP_EXEC);
+	bp_base = (void *)__pkvm_create_private_mapping(phys, __BP_HARDEN_HYP_VECS_SZ,
+							PAGE_SIZE, PAGE_HYP_EXEC);
 	if (IS_ERR_OR_NULL(bp_base))
 		return PTR_ERR(bp_base);
 
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index e5abcce44ad0..18a711d6a52f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -505,7 +505,7 @@ int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
 
 	if (!kvm_host_owns_hyp_mappings()) {
 		addr = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
-					 phys_addr, size, prot);
+					 phys_addr, size, align, prot);
 		if (IS_ERR_OR_NULL((void *)addr))
 			return PTR_ERR((void *)addr);
 		*haddr = addr;
-- 
2.35.1.473.g83b2b277ed-goog