Re: [PATCH v2 1/1] target/riscv: log guest errors when reserved bits are set in PTEs

[Daniel Henrique Barboza]

On 2/3/25 3:18 AM, julia wrote:

For instance, QEMUs newer than b6ecc63c569bb88c0fcadf79fb92bf4b88aefea8
would silently treat this akin to an unmapped page (as required by the
RISC-V spec, admittedly). However, not all hardware platforms do (e.g.
CVA6) which leads to an apparent QEMU bug.

Instead, log a guest error so that in future, incorrectly set up page
tables can be debugged without bisecting QEMU.

Signed-off-by: julia <midni...@trainwit.ch>
---

Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com>

  target/riscv/cpu_helper.c | 27 ++++++++++++++++++++++++++-
  1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index e1dfc4ecbf..3dd8e06044 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -1226,14 +1226,27 @@ restart:
              ppn = pte >> PTE_PPN_SHIFT;
          } else {
              if (pte & PTE_RESERVED) {
+                qemu_log_mask(LOG_GUEST_ERROR, "%s: reserved bits set in PTE: "
+                              "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx 
"\n",
+                              __func__, pte_addr, pte);
                  return TRANSLATE_FAIL;
              }

if (!pbmte && (pte & PTE_PBMT)) {

+                /* Reserved without Svpbmt. */
+                qemu_log_mask(LOG_GUEST_ERROR, "%s: PBMT bits set in PTE, "
+                              "and Svpbmt extension is disabled: "
+                              "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx 
"\n",
+                              __func__, pte_addr, pte);
                  return TRANSLATE_FAIL;
              }

if (!riscv_cpu_cfg(env)->ext_svnapot && (pte & PTE_N)) {

+                /* Reserved without Svnapot extension */
+                qemu_log_mask(LOG_GUEST_ERROR, "%s: N bit set in PTE, "
+                              "and Svnapot extension is disabled: "
+                              "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx 
"\n",
+                              __func__, pte_addr, pte);
                  return TRANSLATE_FAIL;
              }

@@ -1244,14 +1257,19 @@ restart:

              /* Invalid PTE */
              return TRANSLATE_FAIL;
          }
+
          if (pte & (PTE_R | PTE_W | PTE_X)) {
              goto leaf;
          }

- /* Inner PTE, continue walking */

          if (pte & (PTE_D | PTE_A | PTE_U | PTE_ATTR)) {
+            /* D, A, and U bits are reserved in non-leaf/inner PTEs */
+            qemu_log_mask(LOG_GUEST_ERROR, "%s: D, A, or U bits set in non-leaf 
PTE: "
+                          "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx 
"\n",
+                          __func__, pte_addr, pte);
              return TRANSLATE_FAIL;
          }
+        /* Inner PTE, continue walking */
          base = ppn << PGSHIFT;
      }

@@ -1261,10 +1279,17 @@ restart:

   leaf:
      if (ppn & ((1ULL << ptshift) - 1)) {
          /* Misaligned PPN */
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: PPN bits in PTE is misaligned: "
+                      "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx "\n",
+                      __func__, pte_addr, pte);
          return TRANSLATE_FAIL;
      }
      if (!pbmte && (pte & PTE_PBMT)) {
          /* Reserved without Svpbmt. */
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: PBMT bits set in PTE, "
+                      "and Svpbmt extension is disabled: "
+                      "addr: 0x%" HWADDR_PRIx " pte: 0x" TARGET_FMT_lx "\n",
+                      __func__, pte_addr, pte);
          return TRANSLATE_FAIL;
      }