[PATCH v2] target/riscv: Add proper two-stage lookup exception detection

[Georg Kotheimer]

The current two-stage lookup detection in riscv_cpu_do_interrupt falls
short of its purpose, as all it checks is whether two-stage address
translation either via the hypervisor-load store instructions or the
MPRV feature would be allowed.

What we really need instead is whether two-stage address translation was
active when the exception was raised. However, in riscv_cpu_do_interrupt
we do not have the information to reliably detect this. Therefore, when
we raise a memory fault exception we have to record whether two-stage
address translation is active.

Signed-off-by: Georg Kotheimer <georg.kotheimer@kernkonzept.com>
---
Unfortunately, I tested the previous version of the patch only against
the RISC-V softmmu target, not against the linux-user target.
I modified the patch, so that the two_stage_lookup is neither present
nor updated for the linux-user target.

 target/riscv/cpu.c        |  1 +
 target/riscv/cpu.h        |  4 ++++
 target/riscv/cpu_helper.c | 21 ++++++++-------------
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ddea8fbeeb..e8c4455525 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -356,6 +356,7 @@ static void riscv_cpu_reset(DeviceState *dev)
     env->mstatus &= ~(MSTATUS_MIE | MSTATUS_MPRV);
     env->mcause = 0;
     env->pc = env->resetvec;
+    env->two_stage_lookup = false;
 #endif
     cs->exception_index = EXCP_NONE;
     env->load_res = -1;
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 0edb2826a2..0a33d387ba 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -213,6 +213,10 @@ struct CPURISCVState {
     target_ulong satp_hs;
     uint64_t mstatus_hs;
 
+    /* Signals whether the current exception occurred with two-stage address
+       translation active. */
+    bool two_stage_lookup;
+
     target_ulong scounteren;
     target_ulong mcounteren;
 
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 2f43939fb6..af00728829 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -605,6 +605,7 @@ static void raise_mmu_exception(CPURISCVState *env, 
target_ulong address,
         g_assert_not_reached();
     }
     env->badaddr = address;
+    env->two_stage_lookup = two_stage;
 }
 
 hwaddr riscv_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
@@ -646,6 +647,8 @@ void riscv_cpu_do_transaction_failed(CPUState *cs, hwaddr 
physaddr,
     }
 
     env->badaddr = addr;
+    env->two_stage_lookup = riscv_cpu_virt_enabled(env) ||
+                            riscv_cpu_two_stage_lookup(mmu_idx);
     riscv_raise_exception(&cpu->env, cs->exception_index, retaddr);
 }
 
@@ -669,6 +672,8 @@ void riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
         g_assert_not_reached();
     }
     env->badaddr = addr;
+    env->two_stage_lookup = riscv_cpu_virt_enabled(env) ||
+                            riscv_cpu_two_stage_lookup(mmu_idx);
     riscv_raise_exception(env, cs->exception_index, retaddr);
 }
 #endif /* !CONFIG_USER_ONLY */
@@ -910,16 +915,8 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         /* handle the trap in S-mode */
         if (riscv_has_ext(env, RVH)) {
             target_ulong hdeleg = async ? env->hideleg : env->hedeleg;
-            bool two_stage_lookup = false;
 
-            if (env->priv == PRV_M ||
-                (env->priv == PRV_S && !riscv_cpu_virt_enabled(env)) ||
-                (env->priv == PRV_U && !riscv_cpu_virt_enabled(env) &&
-                    get_field(env->hstatus, HSTATUS_HU))) {
-                    two_stage_lookup = true;
-            }
-
-            if ((riscv_cpu_virt_enabled(env) || two_stage_lookup) && 
write_tval) {
+            if (env->two_stage_lookup && write_tval) {
                 /*
                  * If we are writing a guest virtual address to stval, set
                  * this to 1. If we are trapping to VS we will set this to 0
@@ -957,10 +954,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
                 riscv_cpu_set_force_hs_excep(env, 0);
             } else {
                 /* Trap into HS mode */
-                if (!two_stage_lookup) {
-                    env->hstatus = set_field(env->hstatus, HSTATUS_SPV,
-                                             riscv_cpu_virt_enabled(env));
-                }
+                env->hstatus = set_field(env->hstatus, HSTATUS_SPV, false);
                 htval = env->guest_phys_fault_addr;
             }
         }
@@ -1016,6 +1010,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
      * RISC-V ISA Specification.
      */
 
+    env->two_stage_lookup = false;
 #endif
     cs->exception_index = EXCP_NONE; /* mark handled to qemu */
 }
-- 
2.31.0