[PATCH v2 14/24] KVM: arm64: Add pcpu fixmap infrastructure at EL2

[Will Deacon]

From: Quentin Perret <qperret at google.com>

We will soon need to temporarily map pages into the hypervisor stage-1
in nVHE protected mode. To do this efficiently, let's introduce a
per-cpu fixmap allowing to map a single page without needing to take any
lock or to allocate memory.

Signed-off-by: Quentin Perret <qperret at google.com>
Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  2 +
 arch/arm64/kvm/hyp/include/nvhe/mm.h          |  4 ++
 arch/arm64/kvm/hyp/nvhe/mem_protect.c         |  1 -
 arch/arm64/kvm/hyp/nvhe/mm.c                  | 72 +++++++++++++++++++
 arch/arm64/kvm/hyp/nvhe/setup.c               |  4 ++
 5 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 3a0817b5c739..d11d9d68a680 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -59,6 +59,8 @@ enum pkvm_component_id {
 	PKVM_ID_HYP,
 };
 
+extern unsigned long hyp_nr_cpus;
+
 int __pkvm_prot_finalize(void);
 int __pkvm_host_share_hyp(u64 pfn);
 int __pkvm_host_unshare_hyp(u64 pfn);
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
index b2ee6d5df55b..882c5711eda5 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
@@ -13,6 +13,10 @@
 extern struct kvm_pgtable pkvm_pgtable;
 extern hyp_spinlock_t pkvm_pgd_lock;
 
+int hyp_create_pcpu_fixmap(void);
+void *hyp_fixmap_map(phys_addr_t phys);
+int hyp_fixmap_unmap(void);
+
 int hyp_create_idmap(u32 hyp_va_bits);
 int hyp_map_vectors(void);
 int hyp_back_vmemmap(phys_addr_t back);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 9baf731736be..a0af23de2640 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -21,7 +21,6 @@
 
 #define KVM_HOST_S2_FLAGS (KVM_PGTABLE_S2_NOFWB | KVM_PGTABLE_S2_IDMAP)
 
-extern unsigned long hyp_nr_cpus;
 struct host_kvm host_kvm;
 
 static struct hyp_pool host_s2_pool;
diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index d3a3b47181de..17d689483ec4 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -14,6 +14,7 @@
 #include <nvhe/early_alloc.h>
 #include <nvhe/gfp.h>
 #include <nvhe/memory.h>
+#include <nvhe/mem_protect.h>
 #include <nvhe/mm.h>
 #include <nvhe/spinlock.h>
 
@@ -24,6 +25,7 @@ struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS];
 unsigned int hyp_memblock_nr;
 
 static u64 __io_map_base;
+static DEFINE_PER_CPU(void *, hyp_fixmap_base);
 
 static int __pkvm_create_mappings(unsigned long start, unsigned long size,
 				  unsigned long phys, enum kvm_pgtable_prot prot)
@@ -212,6 +214,76 @@ int hyp_map_vectors(void)
 	return 0;
 }
 
+void *hyp_fixmap_map(phys_addr_t phys)
+{
+	void *addr = *this_cpu_ptr(&hyp_fixmap_base);
+	int ret = kvm_pgtable_hyp_map(&pkvm_pgtable, (u64)addr, PAGE_SIZE,
+				      phys, PAGE_HYP);
+	return ret ? NULL : addr;
+}
+
+int hyp_fixmap_unmap(void)
+{
+	void *addr = *this_cpu_ptr(&hyp_fixmap_base);
+	int ret = kvm_pgtable_hyp_unmap(&pkvm_pgtable, (u64)addr, PAGE_SIZE);
+
+	return (ret != PAGE_SIZE) ? -EINVAL : 0;
+}
+
+static int __pin_pgtable_cb(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
+			    enum kvm_pgtable_walk_flags flag, void * const arg)
+{
+	if (!kvm_pte_valid(*ptep) || level != KVM_PGTABLE_MAX_LEVELS - 1)
+		return -EINVAL;
+	hyp_page_ref_inc(hyp_virt_to_page(ptep));
+
+	return 0;
+}
+
+static int hyp_pin_pgtable_pages(u64 addr)
+{
+	struct kvm_pgtable_walker walker = {
+		.cb	= __pin_pgtable_cb,
+		.flags	= KVM_PGTABLE_WALK_LEAF,
+	};
+
+	return kvm_pgtable_walk(&pkvm_pgtable, addr, PAGE_SIZE, &walker);
+}
+
+int hyp_create_pcpu_fixmap(void)
+{
+	unsigned long addr, i;
+	int ret;
+
+	for (i = 0; i < hyp_nr_cpus; i++) {
+		ret = pkvm_alloc_private_va_range(PAGE_SIZE, &addr);
+		if (ret)
+			return ret;
+
+		/*
+		 * Create a dummy mapping, to get the intermediate page-table
+		 * pages allocated, then take a reference on the last level
+		 * page to keep it around at all times.
+		 */
+		ret = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, PAGE_SIZE,
+					  __hyp_pa(__hyp_bss_start), PAGE_HYP);
+		if (ret)
+			return ret;
+
+		ret = hyp_pin_pgtable_pages(addr);
+		if (ret)
+			return ret;
+
+		ret = kvm_pgtable_hyp_unmap(&pkvm_pgtable, addr, PAGE_SIZE);
+		if (ret != PAGE_SIZE)
+			return -EINVAL;
+
+		*per_cpu_ptr(&hyp_fixmap_base, i) = (void *)addr;
+	}
+
+	return 0;
+}
+
 int hyp_create_idmap(u32 hyp_va_bits)
 {
 	unsigned long start, end;
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index fb0eff15a89f..3f689ffb2693 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -321,6 +321,10 @@ void __noreturn __pkvm_init_finalise(void)
 	if (ret)
 		goto out;
 
+	ret = hyp_create_pcpu_fixmap();
+	if (ret)
+		goto out;
+
 	hyp_shadow_table_init(shadow_table_base);
 out:
 	/*
-- 
2.37.0.rc0.161.g10f37bed90-goog