KVM: arm64: Add offset for hyp VA <-> PA conversion

Add a host-initialized constant to KVM nVHE hyp code for converting
between EL2 linear map virtual addresses and physical addresses.
Also add `__hyp_pa` macro that performs the conversion.

Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201202184122.26046-18-dbrazdil@google.com

arch/arm64/kvm/hyp/nvhe/psci-relay.c

@@ -18,6 +18,9 @@
 /* Config options set by the host. */
 __ro_after_init u32 kvm_host_psci_version;
 __ro_after_init struct psci_0_1_function_ids kvm_host_psci_0_1_function_ids;
+__ro_after_init s64 hyp_physvirt_offset;
+
+#define __hyp_pa(x) ((phys_addr_t)((x)) + hyp_physvirt_offset)
 
 static u64 get_psci_func_id(struct kvm_cpu_context *host_ctxt)
 {

arch/arm64/kvm/va_layout.c

@@ -23,6 +23,30 @@ static u8 tag_lsb;
 static u64 tag_val;
 static u64 va_mask;
 
+/*
+ * Compute HYP VA by using the same computation as kern_hyp_va().
+ */
+static u64 __early_kern_hyp_va(u64 addr)
+{
+	addr &= va_mask;
+	addr |= tag_val << tag_lsb;
+	return addr;
+}
+
+/*
+ * Store a hyp VA <-> PA offset into a hyp-owned variable.
+ */
+static void init_hyp_physvirt_offset(void)
+{
+	extern s64 kvm_nvhe_sym(hyp_physvirt_offset);
+	u64 kern_va, hyp_va;
+
+	/* Compute the offset from the hyp VA and PA of a random symbol. */
+	kern_va = (u64)kvm_ksym_ref(__hyp_text_start);
+	hyp_va = __early_kern_hyp_va(kern_va);
+	CHOOSE_NVHE_SYM(hyp_physvirt_offset) = (s64)__pa(kern_va) - (s64)hyp_va;
+}
+
 /*
  * We want to generate a hyp VA with the following format (with V ==
  * vabits_actual):
@@ -54,6 +78,8 @@ __init void kvm_compute_layout(void)
 		tag_val |= get_random_long() & GENMASK_ULL(vabits_actual - 2, tag_lsb);
 	}
 	tag_val >>= tag_lsb;
+
+	init_hyp_physvirt_offset();
 }
 
 static u32 compute_instruction(int n, u32 rd, u32 rn)
@@ -151,9 +177,7 @@ void kvm_patch_vector_branch(struct alt_instr *alt,
 	/*
 	 * Compute HYP VA by using the same computation as kern_hyp_va()
 	 */
-	addr = (uintptr_t)kvm_ksym_ref(__kvm_hyp_vector);
-	addr &= va_mask;
-	addr |= tag_val << tag_lsb;
+	addr = __early_kern_hyp_va((u64)kvm_ksym_ref(__kvm_hyp_vector));
 
 	/* Use PC[10:7] to branch to the same vector in KVM */
 	addr |= ((u64)origptr & GENMASK_ULL(10, 7));