Re: [RFC v9 22/32] target/arm: do not use cc->do_interrupt for KVM directly

[Alex Bennée]

Claudio Fontana <cfontana@suse.de> writes:

> cc->do_interrupt is in theory a TCG callback used in accel/tcg only,
> to prepare the emulated architecture to take an interrupt as defined
> in the hardware specifications,
>
> but in reality the _do_interrupt style of functions in targets are
> also occasionally reused by KVM to prepare the architecture state in a
> similar way where userspace code has identified that it needs to
> deliver an exception to the guest.
>
> In the case of ARM, that includes:
>
> 1) the vcpu thread got a SIGBUS indicating a memory error,
>    and we need to deliver a Synchronous External Abort to the guest to
>    let it know about the error.
> 2) the kernel told us about a debug exception (breakpoint, watchpoint)
>    but it is not for one of QEMU's own gdbstub breakpoints/watchpoints
>    so it must be a breakpoint the guest itself has set up, therefore
>    we need to deliver it to the guest.
>
> So in order to reuse code, the same arm_do_interrupt function is used.
> This is all fine, but we need to avoid calling it using the callback
> registered in CPUClass, since that one is now TCG-only.
>
> Fortunately this is easily solved by replacing calls to
> CPUClass::do_interrupt() with explicit calls to arm_do_interrupt().

My ultra-modern gcc10 gentoo box is quick to point out:

  64.c.o -c ../../target/arm/kvm64.c
  ../../target/arm/kvm64.c: In function ‘kvm_inject_arm_sea’:
  ../../target/arm/kvm64.c:947:15: error: unused variable ‘cc’ 
[-Werror=unused-variable]
    947 |     CPUClass *cc = CPU_GET_CLASS(c);
        |               ^~
  ../../target/arm/kvm64.c: In function ‘kvm_arm_handle_debug’:
  ../../target/arm/kvm64.c:1494:15: error: unused variable ‘cc’ 
[-Werror=unused-variable]
   1494 |     CPUClass *cc = CPU_GET_CLASS(cs);
        |               ^~
  cc1: all warnings being treated as errors


>
> Signed-off-by: Claudio Fontana <cfontana@suse.de>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  target/arm/helper.c | 4 ++++
>  target/arm/kvm64.c  | 4 ++--
>  2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index 38cd35c049..bebaabf525 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -9895,6 +9895,10 @@ static void handle_semihosting(CPUState *cs)
>   * Do any appropriate logging, handle PSCI calls, and then hand off
>   * to the AArch64-entry or AArch32-entry function depending on the
>   * target exception level's register width.
> + *
> + * Note: this is used for both TCG (as the do_interrupt tcg op),
> + *       and KVM to re-inject guest debug exceptions, and to
> + *       inject a Synchronous-External-Abort.
>   */
>  void arm_cpu_do_interrupt(CPUState *cs)
>  {
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index f74bac2457..2b17e4203d 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -960,7 +960,7 @@ static void kvm_inject_arm_sea(CPUState *c)
>  
>      env->exception.syndrome = esr;
>  
> -    cc->do_interrupt(c);
> +    arm_cpu_do_interrupt(c);
>  }
>  
>  #define AARCH64_CORE_REG(x)   (KVM_REG_ARM64 | KVM_REG_SIZE_U64 | \
> @@ -1545,7 +1545,7 @@ bool kvm_arm_handle_debug(CPUState *cs, struct 
> kvm_debug_exit_arch *debug_exit)
>      env->exception.vaddress = debug_exit->far;
>      env->exception.target_el = 1;
>      qemu_mutex_lock_iothread();
> -    cc->do_interrupt(cs);
> +    arm_cpu_do_interrupt(cs);
>      qemu_mutex_unlock_iothread();
>  
>      return false;


-- 
Alex Bennée