[PATCH v2 13/16] arm64: Implement ioremap/iounmap hooks calling into KVM's MMIO guard

[Marc Zyngier <maz@kernel.org>]

Implement the previously defined ioremap/iounmap hooks for arm64,
calling into KVM's MMIO guard if available.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/mm/ioremap.c | 112 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)

diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
index b7c81dacabf0..5334cbdc9f64 100644
--- a/arch/arm64/mm/ioremap.c
+++ b/arch/arm64/mm/ioremap.c
@@ -9,13 +9,125 @@
  * Copyright (C) 2012 ARM Ltd.
  */
 
+#define pr_fmt(fmt)	"ioremap: " fmt
+
 #include <linux/export.h>
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
+#include <linux/slab.h>
 #include <linux/io.h>
+#include <linux/arm-smccc.h>
 
 #include <asm/fixmap.h>
 #include <asm/tlbflush.h>
+#include <asm/hypervisor.h>
+
+struct ioremap_guard_ref {
+	refcount_t	count;
+};
+
+static DEFINE_STATIC_KEY_FALSE(ioremap_guard_key);
+static DEFINE_XARRAY(ioremap_guard_array);
+static DEFINE_MUTEX(ioremap_guard_lock);
+
+void ioremap_phys_range_hook(phys_addr_t phys_addr, size_t size, pgprot_t prot)
+{
+	if (!static_branch_unlikely(&ioremap_guard_key))
+		return;
+
+	if (pfn_valid(__phys_to_pfn(phys_addr)))
+		return;
+
+	mutex_lock(&ioremap_guard_lock);
+
+	while (size) {
+		u64 pfn = phys_addr >> PAGE_SHIFT;
+		struct ioremap_guard_ref *ref;
+		struct arm_smccc_res res;
+
+		ref = xa_load(&ioremap_guard_array, pfn);
+		if (ref) {
+			refcount_inc(&ref->count);
+			goto next;
+		}
+
+		/*
+		 * It is acceptable for the allocation to fail, specially
+		 * if trying to ioremap something very early on, like with
+		 * earlycon, which happens long before kmem_cache_init.
+		 * This page will be permanently accessible, similar to a
+		 * saturated refcount.
+		 */
+		ref = kzalloc(sizeof(*ref), GFP_KERNEL);
+		if (ref) {
+			refcount_set(&ref->count, 1);
+			if (xa_err(xa_store(&ioremap_guard_array, pfn, ref,
+					    GFP_KERNEL))) {
+				kfree(ref);
+				ref = NULL;
+			}
+		}
+
+		arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_MAP_FUNC_ID,
+				  phys_addr, prot, &res);
+		if (res.a0 != SMCCC_RET_SUCCESS) {
+			pr_warn_ratelimited("Failed to register %llx\n",
+					    phys_addr);
+			xa_erase(&ioremap_guard_array, pfn);
+			kfree(ref);
+			goto out;
+		}
+
+	next:
+		size -= PAGE_SIZE;
+		phys_addr += PAGE_SIZE;
+	}
+out:
+	mutex_unlock(&ioremap_guard_lock);
+}
+
+void iounmap_phys_range_hook(phys_addr_t phys_addr, size_t size)
+{
+	if (!static_branch_unlikely(&ioremap_guard_key))
+		return;
+
+	VM_BUG_ON(phys_addr & ~PAGE_MASK || size & ~PAGE_MASK);
+
+	mutex_lock(&ioremap_guard_lock);
+
+	while (size) {
+		u64 pfn = phys_addr >> PAGE_SHIFT;
+		struct ioremap_guard_ref *ref;
+		struct arm_smccc_res res;
+
+		ref = xa_load(&ioremap_guard_array, pfn);
+		if (!ref) {
+			pr_warn_ratelimited("%llx not tracked, left mapped\n",
+					    phys_addr);
+			goto next;
+		}
+
+		if (!refcount_dec_and_test(&ref->count))
+			goto next;
+
+		xa_erase(&ioremap_guard_array, pfn);
+		kfree(ref);
+
+		arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_UNMAP_FUNC_ID,
+				  phys_addr, &res);
+		if (res.a0 != SMCCC_RET_SUCCESS) {
+			pr_warn_ratelimited("Failed to unregister %llx\n",
+					    phys_addr);
+			goto out;
+		}
+
+	next:
+		size -= PAGE_SIZE;
+		phys_addr += PAGE_SIZE;
+	}
+out:
+	mutex_unlock(&ioremap_guard_lock);
+}
 
 static void __iomem *__ioremap_caller(phys_addr_t phys_addr, size_t size,
 				      pgprot_t prot, void *caller)
-- 
2.30.2