[13/16] hw/arm/boot: Don't write secondary boot stub if using PSCI

Commit Message

Peter Maydell Jan. 27, 2022, 3:46 p.m. UTC

If we're using PSCI emulation to start secondary CPUs, there is no
point in writing the "secondary boot" stub code, because it will
never be used -- secondary CPUs start powered-off, and when powered
on are set to begin execution at the address specified by the guest's
power-on PSCI call, not at the stub.

Move the call to the hook that writes the secondary boot stub code so
that we can do it only if we're starting a Linux kernel and not using
PSCI.

(None of the users of the hook care about the ordering of its call
relative to anything else: they only use it to write a rom blob to
guest memory.)

Signed-off-by: Peter Maydell <[e-mail]>
---
 include/hw/arm/boot.h |  3 +++
 hw/arm/boot.c         | 35 ++++++++++++++++++++++++-----------
 2 files changed, 27 insertions(+), 11 deletions(-)

Comments

Richard Henderson Jan. 31, 2022, 8:06 a.m. UTC | #1

On 1/28/22 02:46, Peter Maydell wrote:
> If we're using PSCI emulation to start secondary CPUs, there is no
> point in writing the "secondary boot" stub code, because it will
> never be used -- secondary CPUs start powered-off, and when powered
> on are set to begin execution at the address specified by the guest's
> power-on PSCI call, not at the stub.
> 
> Move the call to the hook that writes the secondary boot stub code so
> that we can do it only if we're starting a Linux kernel and not using
> PSCI.
> 
> (None of the users of the hook care about the ordering of its call
> relative to anything else: they only use it to write a rom blob to
> guest memory.)
> 
> Signed-off-by: Peter Maydell<[e-mail]>
> ---
>   include/hw/arm/boot.h |  3 +++
>   hw/arm/boot.c         | 35 ++++++++++++++++++++++++-----------
>   2 files changed, 27 insertions(+), 11 deletions(-)

Reviewed-by: Richard Henderson <[e-mail]>

r~

Patch

diff --git a/include/hw/arm/boot.h b/include/hw/arm/boot.h
index 0bcb58babba..0cfc1c95c4e 100644
--- a/include/hw/arm/boot.h
+++ b/include/hw/arm/boot.h
@@ -70,6 +70,9 @@  struct arm_boot_info {
      * boot loader/boot ROM code, and secondary_cpu_reset_hook() should
      * perform any necessary CPU reset handling and set the PC for the
      * secondary CPUs to point at this boot blob.
+     *
+     * These hooks won't be called if secondary CPUs are booting via
+     * emulated PSCI (see psci_conduit below).
      */
     void (*write_secondary_boot)(ARMCPU *cpu,
                                  const struct arm_boot_info *info);
diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index 0424c178305..184628ce564 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -804,7 +804,7 @@  static void do_cpu_reset(void *opaque)
                         set_kernel_args(info, as);
                     }
                 }
-            } else {
+            } else if (info->secondary_cpu_reset_hook) {
                 info->secondary_cpu_reset_hook(cpu, info);
             }
         }
@@ -1030,13 +1030,6 @@  static void arm_setup_direct_kernel_boot(ARMCPU *cpu,
         elf_machine = EM_ARM;
     }
 
-    if (!info->secondary_cpu_reset_hook) {
-        info->secondary_cpu_reset_hook = default_reset_secondary;
-    }
-    if (!info->write_secondary_boot) {
-        info->write_secondary_boot = default_write_secondary;
-    }
-
     if (info->nb_cpus == 0)
         info->nb_cpus = 1;
 
@@ -1216,9 +1209,6 @@  static void arm_setup_direct_kernel_boot(ARMCPU *cpu,
         write_bootloader("bootloader", info->loader_start,
                          primary_loader, fixupcontext, as);
 
-        if (info->nb_cpus > 1) {
-            info->write_secondary_boot(cpu, info);
-        }
         if (info->write_board_setup) {
             info->write_board_setup(cpu, info);
         }
@@ -1385,6 +1375,29 @@  void arm_load_kernel(ARMCPU *cpu, MachineState *ms, struct arm_boot_info *info)
         }
     }
 
+    if (info->psci_conduit == QEMU_PSCI_CONDUIT_DISABLED &&
+        info->is_linux && info->nb_cpus > 1) {
+        /*
+         * We're booting Linux but not using PSCI, so for SMP we need
+         * to write a custom secondary CPU boot loader stub, and arrange
+         * for the secondary CPU reset to make the accompanying initialization.
+         */
+        if (!info->secondary_cpu_reset_hook) {
+            info->secondary_cpu_reset_hook = default_reset_secondary;
+        }
+        if (!info->write_secondary_boot) {
+            info->write_secondary_boot = default_write_secondary;
+        }
+        info->write_secondary_boot(cpu, info);
+    } else {
+        /*
+         * No secondary boot stub; don't use the reset hook that would
+         * have set the CPU up to call it
+         */
+        info->write_secondary_boot = NULL;
+        info->secondary_cpu_reset_hook = NULL;
+    }
+
     /*
      * arm_load_dtb() may add a PSCI node so it must be called after we have
      * decided whether to enable PSCI and set the psci-conduit CPU properties.