KVM: arm64: Elevate hypervisor mappings creation at EL2

Previous commits have introduced infrastructure to enable the EL2 code
to manage its own stage 1 mappings. However, this was preliminary work,
and none of it is currently in use.

Put all of this together by elevating the mapping creation at EL2 when
memory protection is enabled. In this case, the host kernel running
at EL1 still creates _temporary_ EL2 mappings, only used while
initializing the hypervisor, but frees them right after.

As such, all calls to create_hyp_mappings() after kvm init has finished
turn into hypercalls, as the host now has no 'legal' way to modify the
hypevisor page tables directly.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-19-qperret@google.com

1 files changed, 38 insertions, 5 deletions

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index e583f7fb3620..de0ad79d2c90 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -221,15 +221,39 @@ void free_hyp_pgds(void)
 	if (hyp_pgtable) {
 		kvm_pgtable_hyp_destroy(hyp_pgtable);
 		kfree(hyp_pgtable);
+		hyp_pgtable = NULL;
 	}
 	mutex_unlock(&kvm_hyp_pgd_mutex);
 }
 
+static bool kvm_host_owns_hyp_mappings(void)
+{
+	if (static_branch_likely(&kvm_protected_mode_initialized))
+		return false;
+
+	/*
+	 * This can happen at boot time when __create_hyp_mappings() is called
+	 * after the hyp protection has been enabled, but the static key has
+	 * not been flipped yet.
+	 */
+	if (!hyp_pgtable && is_protected_kvm_enabled())
+		return false;
+
+	WARN_ON(!hyp_pgtable);
+
+	return true;
+}
+
 static int __create_hyp_mappings(unsigned long start, unsigned long size,
 				 unsigned long phys, enum kvm_pgtable_prot prot)
 {
 	int err;
 
+	if (!kvm_host_owns_hyp_mappings()) {
+		return kvm_call_hyp_nvhe(__pkvm_create_mappings,
+					 start, size, phys, prot);
+	}
+
 	mutex_lock(&kvm_hyp_pgd_mutex);
 	err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot);
 	mutex_unlock(&kvm_hyp_pgd_mutex);
@@ -291,6 +315,16 @@ static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
 	unsigned long base;
 	int ret = 0;
 
+	if (!kvm_host_owns_hyp_mappings()) {
+		base = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
+					 phys_addr, size, prot);
+		if (IS_ERR_OR_NULL((void *)base))
+			return PTR_ERR((void *)base);
+		*haddr = base;
+
+		return 0;
+	}
+
 	mutex_lock(&kvm_hyp_pgd_mutex);
 
 	/*
@@ -1270,10 +1304,9 @@ static struct kvm_pgtable_mm_ops kvm_hyp_mm_ops = {
 	.virt_to_phys		= kvm_host_pa,
 };
 
-int kvm_mmu_init(void)
+int kvm_mmu_init(u32 *hyp_va_bits)
 {
 	int err;
-	u32 hyp_va_bits;
 
 	hyp_idmap_start = __pa_symbol(__hyp_idmap_text_start);
 	hyp_idmap_start = ALIGN_DOWN(hyp_idmap_start, PAGE_SIZE);
@@ -1287,8 +1320,8 @@ int kvm_mmu_init(void)
 	 */
 	BUG_ON((hyp_idmap_start ^ (hyp_idmap_end - 1)) & PAGE_MASK);
 
-	hyp_va_bits = 64 - ((idmap_t0sz & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET);
-	kvm_debug("Using %u-bit virtual addresses at EL2\n", hyp_va_bits);
+	*hyp_va_bits = 64 - ((idmap_t0sz & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET);
+	kvm_debug("Using %u-bit virtual addresses at EL2\n", *hyp_va_bits);
 	kvm_debug("IDMAP page: %lx\n", hyp_idmap_start);
 	kvm_debug("HYP VA range: %lx:%lx\n",
 		  kern_hyp_va(PAGE_OFFSET),
@@ -1313,7 +1346,7 @@ int kvm_mmu_init(void)
 		goto out;
 	}
 
-	err = kvm_pgtable_hyp_init(hyp_pgtable, hyp_va_bits, &kvm_hyp_mm_ops);
+	err = kvm_pgtable_hyp_init(hyp_pgtable, *hyp_va_bits, &kvm_hyp_mm_ops);
 	if (err)
 		goto out_free_pgtable;