[PATCH] target/riscv: fix check of guest pa top bits

[Jose Martins]

The spec states that on sv39x4 guest physical  "address bits 63:41
must all be zeros, or else a guest-page-fault exception occurs.".
However, the check performed for these top bits of the virtual address
on the second stage is the same as the one performed for virtual
addresses on the first stage except with the 2-bit extension,
effectively creating the same kind of "hole" in the guest's physical
address space. I believe the following patch fixes this issue:

Signed-off-by: Jose Martins <josemartin...@gmail.com>
---
 target/riscv/cpu_helper.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index d3ba9efb02..da879f5656 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -421,15 +421,21 @@ static int get_physical_address(CPURISCVState
*env, hwaddr *physical,
     int va_bits = PGSHIFT + levels * ptidxbits + widened;
     target_ulong mask, masked_msbs;

-    if (TARGET_LONG_BITS > (va_bits - 1)) {
-        mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
+    if(!first_stage){
+        if ((addr >> va_bits) != 0) {
+            return TRANSLATE_FAIL;
+        }
     } else {
-        mask = 0;
-    }
-    masked_msbs = (addr >> (va_bits - 1)) & mask;
+        if (TARGET_LONG_BITS > (va_bits - 1)) {
+            mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
+        } else {
+            mask = 0;
+        }
+        masked_msbs = (addr >> (va_bits - 1)) & mask;

-    if (masked_msbs != 0 && masked_msbs != mask) {
-        return TRANSLATE_FAIL;
+        if (masked_msbs != 0 && masked_msbs != mask) {
+            return TRANSLATE_FAIL;
+        }
     }

     int ptshift = (levels - 1) * ptidxbits;
-- 
2.17.1

Jose