KVM: arm64: Fix nVHE stacktrace VA bits mask

The hypervisor VA space size depends on both the ID map's
(IDMAP_VA_BITS) and the kernel stage-1 (VA_BITS). However, the
hypervisor stacktrace decoding is solely relying on VA_BITS. This is
especially an issue when VA_BITS < IDMAP_VA_BITS (i.e. VA_BITS is
39-bit): the hypervisor may have addresses bigger than the stacktrace is
masking.

Align this mask with hyp_va_bits.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://lore.kernel.org/r/20250107112821.416591-1-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_mmu.h

@@ -139,6 +139,8 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
 
 #define kern_hyp_va(v) 	((typeof(v))(__kern_hyp_va((unsigned long)(v))))
 
+extern u32 __hyp_va_bits;
+
 /*
  * We currently support using a VM-specified IPA size. For backward
  * compatibility, the default IPA size is fixed to 40bits.

arch/arm64/kvm/mmu.c

@@ -29,6 +29,8 @@ static unsigned long __ro_after_init hyp_idmap_start;
 static unsigned long __ro_after_init hyp_idmap_end;
 static phys_addr_t __ro_after_init hyp_idmap_vector;
 
+u32 __ro_after_init __hyp_va_bits;
+
 static unsigned long __ro_after_init io_map_base;
 
 static phys_addr_t __stage2_range_addr_end(phys_addr_t addr, phys_addr_t end,
@@ -2056,6 +2058,7 @@ int __init kvm_mmu_init(u32 *hyp_va_bits)
 		goto out_destroy_pgtable;
 
 	io_map_base = hyp_idmap_start;
+	__hyp_va_bits = *hyp_va_bits;
 	return 0;
 
 out_destroy_pgtable:

arch/arm64/kvm/stacktrace.c

@@ -19,6 +19,7 @@
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>
 
+#include <asm/kvm_mmu.h>
 #include <asm/stacktrace/nvhe.h>
 
 static struct stack_info stackinfo_get_overflow(void)
@@ -145,7 +146,7 @@ static void unwind(struct unwind_state *state,
  */
 static bool kvm_nvhe_dump_backtrace_entry(void *arg, unsigned long where)
 {
-	unsigned long va_mask = GENMASK_ULL(vabits_actual - 1, 0);
+	unsigned long va_mask = GENMASK_ULL(__hyp_va_bits - 1, 0);
 	unsigned long hyp_offset = (unsigned long)arg;
 
 	/* Mask tags and convert to kern addr */