Re: [PATCH v2 04/18] exec: Add RISC-V WorldGuard WID to MemTxAttrs

[Daniel Henrique Barboza]

On 10/8/25 2:54 AM, Jim Shu wrote:

Hi Daniel,

Both '_reserved1' and '_reserved2' fields are only for padding
MemTxAttrs struct to be 8-byte [1], so I remove a 1-byte reserved
field when adding 'world_id' field to it.
Is it ok for you? Or you think it is better to separate them.

It's fine. I suggest adding this explanation in the commit msg to avoid
further questions about it.


Thanks,

Daniel

[1]
commit 5014e33b1e00d330f13df33c09a3932ac88f8d94
Link: https://lore.kernel.org/r/20250121151322.171832-2-zhao1....@intel.com

Thanks!

On Sat, Aug 9, 2025 at 8:34 PM Daniel Henrique Barboza
<dbarb...@ventanamicro.com> wrote:

On 4/17/25 7:52 AM, Jim Shu wrote:

RISC-V WorldGuard will add 5-bit world_id (WID) to the each memory
transaction on the bus. The wgChecker in front of RAM or peripherals
MMIO could do the access control based on the WID. It is similar to ARM
TrustZone NS bit, but the WID is 5-bit.

The common implementation of WID is AXI4 AxUSER signal.

Signed-off-by: Jim Shu <jim....@sifive.com>
---
   include/exec/memattrs.h | 8 ++++++--
   1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/exec/memattrs.h b/include/exec/memattrs.h
index 8db1d30464..7a6866fa41 100644
--- a/include/exec/memattrs.h
+++ b/include/exec/memattrs.h
@@ -54,6 +54,11 @@ typedef struct MemTxAttrs {
        */
       unsigned int pid:8;

+    /*
+     * RISC-V WorldGuard: the 5-bit WID field of memory access.
+     */
+    unsigned int world_id:5;
+
       /*
        * Bus masters which don't specify any attributes will get this
        * (via the MEMTXATTRS_UNSPECIFIED constant), so that we can
@@ -63,8 +68,7 @@ typedef struct MemTxAttrs {
        */
       bool unspecified;

-    uint8_t _reserved1;
-    uint16_t _reserved2;
+    uint16_t _reserved1;

Is 'reserved2' unused? Not sure why you ended up removing it in this patch.

If it's really unused it's ok to remove it but this should be done in separate.


Thanks,

Daniel

   } MemTxAttrs;

   QEMU_BUILD_BUG_ON(sizeof(MemTxAttrs) > 8);