[PATCH v4 4/8] KVM: arm64: Add guard pages for pKVM (protected nVHE) hypervisor stack

[Kalesh Singh]

Maps the stack pages in the flexible private VA range and allocates
guard pages below the stack as unbacked VA space. The stack is aligned
to twice its size to aid overflow detection (implemented in a subsequent
patch in the series).

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---

Changes in v4:
  - Replace IS_ERR_OR_NULL check with IS_ERR check now that
    pkvm_alloc_private_va_range() returns an error for null
    pointer, per Fuad

Changes in v3:
  - Handle null ptr in IS_ERR_OR_NULL checks, per Mark

 arch/arm64/kvm/hyp/nvhe/setup.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 27af337f9fea..1b69a25c1861 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -105,11 +105,28 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 		if (ret)
 			return ret;
 
-		end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va;
+		/*
+		 * Private mappings are allocated upwards from __io_map_base
+		 * so allocate the guard page first then the stack.
+		 */
+		start = (void *)pkvm_alloc_private_va_range(PAGE_SIZE, PAGE_SIZE);
+		if (IS_ERR(start))
+			return PTR_ERR(start);
+
+		/*
+		 * The stack is aligned to twice its size to facilitate overflow
+		 * detection.
+		 */
+		end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_pa;
 		start = end - PAGE_SIZE;
-		ret = pkvm_create_mappings(start, end, PAGE_HYP);
-		if (ret)
-			return ret;
+		start = (void *)__pkvm_create_private_mapping((phys_addr_t)start,
+					PAGE_SIZE, PAGE_SIZE * 2, PAGE_HYP);
+		if (IS_ERR(start))
+			return PTR_ERR(start);
+		end = start + PAGE_SIZE;
+
+		/* Update stack_hyp_va to end of the stack's private VA range */
+		per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va = (unsigned long) end;
 	}
 
 	/*
-- 
2.35.1.574.g5d30c73bfb-goog