Re: [Qemu-devel] [PATCH 2/5] user-exec: Push resume-from-signal code out to handle_cpu_signal()

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 16/05/16 19:09, Peter Maydell wrote:
> Since the only caller of page_unprotect() which might cause it to
> need to call cpu_resume_from_signal() is handle_cpu_signal() in
> the user-mode code, push the longjump handling out to that function.
>
> Since this is the only caller of cpu_resume_from_signal() which
> passes a non-NULL puc argument, split the non-NULL handling into
> a new cpu_exit_tb_from_sighandler() function. This allows us
> to merge the softmmu and usermode implementations of the
> cpu_resume_from_signal() function, which are now identical.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Sergey Fedorov <sergey.fedorov@linaro.org>

> ---
>  cpu-exec-common.c |  2 +-
>  translate-all.c   | 12 ++++++++----
>  translate-all.h   |  2 +-
>  user-exec.c       | 41 +++++++++++++++++++++++++++++------------
>  4 files changed, 39 insertions(+), 18 deletions(-)
>
> diff --git a/cpu-exec-common.c b/cpu-exec-common.c
> index 6bdda6b..62f5d6b 100644
> --- a/cpu-exec-common.c
> +++ b/cpu-exec-common.c
> @@ -28,7 +28,6 @@ CPUState *tcg_current_cpu;
>  /* exit the current TB from a signal handler. The host registers are
>     restored in a state compatible with the CPU emulator
>   */
> -#if defined(CONFIG_SOFTMMU)
>  void cpu_resume_from_signal(CPUState *cpu, void *puc)
>  {
>      /* XXX: restore cpu registers saved in host registers */
> @@ -37,6 +36,7 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
>      siglongjmp(cpu->jmp_env, 1);
>  }
>  
> +#if defined(CONFIG_SOFTMMU)
>  void cpu_reloading_memory_map(void)
>  {
>      if (qemu_in_vcpu_thread()) {
> diff --git a/translate-all.c b/translate-all.c
> index 4820d2e..52a571e 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -1955,7 +1955,7 @@ int page_check_range(target_ulong start, target_ulong len, int flags)
>              /* unprotect the page if it was put read-only because it
>                 contains translated code */
>              if (!(p->flags & PAGE_WRITE)) {
> -                if (!page_unprotect(addr, 0, NULL)) {
> +                if (!page_unprotect(addr, 0)) {
>                      return -1;
>                  }
>              }
> @@ -1965,8 +1965,12 @@ int page_check_range(target_ulong start, target_ulong len, int flags)
>  }
>  
>  /* called from signal handler: invalidate the code and unprotect the
> -   page. Return TRUE if the fault was successfully handled. */
> -int page_unprotect(target_ulong address, uintptr_t pc, void *puc)
> + * page. Return 0 if the fault was not handled, 1 if it was handled,
> + * and 2 if it was handled but the caller must cause the TB to be
> + * immediately exited. (We can only return 2 if the 'pc' argument is
> + * non-zero.)
> + */
> +int page_unprotect(target_ulong address, uintptr_t pc)
>  {
>      unsigned int prot;
>      PageDesc *p;
> @@ -1999,7 +2003,7 @@ int page_unprotect(target_ulong address, uintptr_t pc, void *puc)
>                 the corresponding translated code. */
>              if (tb_invalidate_phys_page(addr, pc)) {
>                  mmap_unlock();
> -                cpu_resume_from_signal(current_cpu, puc);
> +                return 2;
>              }
>  #ifdef DEBUG_TB_CHECK
>              tb_invalidate_check(addr);
> diff --git a/translate-all.h b/translate-all.h
> index 0384640..ce6071b 100644
> --- a/translate-all.h
> +++ b/translate-all.h
> @@ -27,7 +27,7 @@ void tb_invalidate_phys_range(tb_page_addr_t start, tb_page_addr_t end);
>  void tb_check_watchpoint(CPUState *cpu);
>  
>  #ifdef CONFIG_USER_ONLY
> -int page_unprotect(target_ulong address, uintptr_t pc, void *puc);
> +int page_unprotect(target_ulong address, uintptr_t pc);
>  #endif
>  
>  #endif /* TRANSLATE_ALL_H */
> diff --git a/user-exec.c b/user-exec.c
> index d8d597b..1d02e24 100644
> --- a/user-exec.c
> +++ b/user-exec.c
> @@ -54,7 +54,7 @@ static void exception_action(CPUState *cpu)
>  /* exit the current TB from a signal handler. The host registers are
>     restored in a state compatible with the CPU emulator
>   */
> -void cpu_resume_from_signal(CPUState *cpu, void *puc)
> +static void cpu_exit_tb_from_sighandler(CPUState *cpu, void *puc)
>  {
>  #ifdef __linux__
>      struct ucontext *uc = puc;
> @@ -62,20 +62,18 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
>      struct sigcontext *uc = puc;
>  #endif
>  
> -    if (puc) {
> -        /* XXX: use siglongjmp ? */
> +    /* XXX: use siglongjmp ? */
>  #ifdef __linux__
>  #ifdef __ia64
> -        sigprocmask(SIG_SETMASK, (sigset_t *)&uc->uc_sigmask, NULL);
> +    sigprocmask(SIG_SETMASK, (sigset_t *)&uc->uc_sigmask, NULL);
>  #else
> -        sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
> +    sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
>  #endif
>  #elif defined(__OpenBSD__)
> -        sigprocmask(SIG_SETMASK, &uc->sc_mask, NULL);
> +    sigprocmask(SIG_SETMASK, &uc->sc_mask, NULL);
>  #endif
> -    }
> -    cpu->exception_index = -1;
> -    siglongjmp(cpu->jmp_env, 1);
> +
> +    cpu_resume_from_signal(cpu, NULL);
>  }
>  
>  /* 'pc' is the host PC at which the exception was raised. 'address' is
> @@ -95,9 +93,28 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned long address,
>             pc, address, is_write, *(unsigned long *)old_set);
>  #endif
>      /* XXX: locking issue */
> -    if (is_write && h2g_valid(address)
> -        && page_unprotect(h2g(address), pc, puc)) {
> -        return 1;
> +    if (is_write && h2g_valid(address)) {
> +        switch (page_unprotect(h2g(address), pc)) {
> +        case 0:
> +            /* Fault not caused by a page marked unwritable to protect
> +             * cached translations, must be the guest binary's problem
> +             */
> +            break;
> +        case 1:
> +            /* Fault caused by protection of cached translation; TBs
> +             * invalidated, so resume execution
> +             */
> +            return 1;
> +        case 2:
> +            /* Fault caused by protection of cached translation, and the
> +             * currently executing TB was modified and must be exited
> +             * immediately.
> +             */
> +            cpu_exit_tb_from_sighandler(current_cpu, puc);
> +            g_assert_not_reached();
> +        default:
> +            g_assert_not_reached();
> +        }
>      }
>  
>      /* Convert forcefully to guest address space, invalid addresses