target/riscv/kvm: Fix exposure of Zkr

The Zkr extension may only be exposed to KVM guests if the VMM
implements the SEED CSR. Use the same implementation as TCG.

Without this patch, running with a KVM which does not forward the
SEED CSR access to QEMU will result in an ILL exception being
injected into the guest (this results in Linux guests crashing on
boot). And, when running with a KVM which does forward the access,
QEMU will crash, since QEMU doesn't know what to do with the exit.

Fixes: 3108e2f1c6 ("target/riscv/kvm: update KVM exts to Linux 6.8")
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Cc: qemu-stable <qemu-stable@nongnu.org>
Message-ID: <20240422134605.534207-2-ajones@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -819,6 +819,9 @@ void riscv_set_csr_ops(int csrno, riscv_csr_operations *ops);
 
 void riscv_cpu_register_gdb_regs_for_features(CPUState *cs);
 
+target_ulong riscv_new_csr_seed(target_ulong new_value,
+                                target_ulong write_mask);
+
 uint8_t satp_mode_max_from_map(uint32_t map);
 const char *satp_mode_str(uint8_t satp_mode, bool is_32_bit);
 

target/riscv/csr.c

@@ -4267,10 +4267,8 @@ static RISCVException write_upmbase(CPURISCVState *env, int csrno,
 #endif
 
 /* Crypto Extension */
-static RISCVException rmw_seed(CPURISCVState *env, int csrno,
+target_ulong riscv_new_csr_seed(target_ulong new_value,
-                               target_ulong *ret_value,
+                                target_ulong write_mask)
-                               target_ulong new_value,
-                               target_ulong write_mask)
 {
     uint16_t random_v;
     Error *random_e = NULL;
@@ -4294,6 +4292,18 @@ static RISCVException rmw_seed(CPURISCVState *env, int csrno,
         rval = random_v | SEED_OPST_ES16;
     }
 
+    return rval;
+}
+
+static RISCVException rmw_seed(CPURISCVState *env, int csrno,
+                               target_ulong *ret_value,
+                               target_ulong new_value,
+                               target_ulong write_mask)
+{
+    target_ulong rval;
+
+    rval = riscv_new_csr_seed(new_value, write_mask);
+
     if (ret_value) {
         *ret_value = rval;
     }

target/riscv/kvm/kvm-cpu.c

@@ -1418,6 +1418,28 @@ static int kvm_riscv_handle_sbi(CPUState *cs, struct kvm_run *run)
     return ret;
 }
 
+static int kvm_riscv_handle_csr(CPUState *cs, struct kvm_run *run)
+{
+    target_ulong csr_num = run->riscv_csr.csr_num;
+    target_ulong new_value = run->riscv_csr.new_value;
+    target_ulong write_mask = run->riscv_csr.write_mask;
+    int ret = 0;
+
+    switch (csr_num) {
+    case CSR_SEED:
+        run->riscv_csr.ret_value = riscv_new_csr_seed(new_value, write_mask);
+        break;
+    default:
+        qemu_log_mask(LOG_UNIMP,
+                      "%s: un-handled CSR EXIT for CSR %lx\n",
+                      __func__, csr_num);
+        ret = -1;
+        break;
+    }
+
+    return ret;
+}
+
 int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
 {
     int ret = 0;
@@ -1425,6 +1447,9 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
     case KVM_EXIT_RISCV_SBI:
         ret = kvm_riscv_handle_sbi(cs, run);
         break;
+    case KVM_EXIT_RISCV_CSR:
+        ret = kvm_riscv_handle_csr(cs, run);
+        break;
     default:
         qemu_log_mask(LOG_UNIMP, "%s: un-handled exit reason %d\n",
                       __func__, run->exit_reason);