[PATCH] target/arm: Implement ARMv8.1-VMID16 extension

[Peter Maydell]

The ARMv8.1-VMID16 extension extends the VMID from 8 bits to 16 bits:

 * the ID_AA64MMFR1_EL1.VMIDBits field specifies whether the VMID is
   8 or 16 bits
 * the VMID field in VTTBR_EL2 is extended to 16 bits
 * VTCR_EL2.VS lets the guest specify whether to use the full 16 bits,
   or use the backwards-compatible 8 bits

For QEMU implementing this is trivial:
 * we do not track VMIDs in TLB entries, so we never use the VMID field
 * we treat any write to VTTBR_EL2, not just a change to the VMID field
   bits, as a "possible VMID change" that causes us to throw away TLB
   entries, so that code doesn't need changing
 * we allow the guest to read/write the VTCR_EL2.VS bit already

So all that's missing is the ID register part: report that we support
VMID16 in our 'max' CPU.

Signed-off-by: Peter Maydell <address@hidden>
---
Not something anybody's been asking for, but worthwhile as
a step towards finishing off support for all the v8.1 extensions.

 target/arm/cpu64.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 2d97bf45e1e..bf2cf278c03 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -672,6 +672,7 @@ static void aarch64_max_initfn(Object *obj)
         t = cpu->isar.id_aa64mmfr1;
         t = FIELD_DP64(t, ID_AA64MMFR1, HPDS, 1); /* HPD */
         t = FIELD_DP64(t, ID_AA64MMFR1, LO, 1);
+        t = FIELD_DP64(t, ID_AA64MMFR1, VMIDBITS, 2); /* VMID16 */
         cpu->isar.id_aa64mmfr1 = t;
 
         /* Replicate the same data to the 32-bit id registers.  */
-- 
2.20.1