Re: [PATCH v4 19/43] accel/tcg: Support split-wx for darwin/iOS with vm_remap

[Joelle van Dyne]

Guarding MAP_JIT with

if (!splitwx) {
    flags |= MAP_JIT;
}

is better because MAP_JIT tells the kernel that we want a RWX mapping
which is not the case. On iOS, special entitlements are needed for
MAP_JIT.

-j

On Mon, Dec 14, 2020 at 6:03 AM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Cribbed from code posted by Joelle van Dyne <j@getutm.app>,
> and rearranged to a cleaner structure.
>
> Reviewed-by: Joelle van Dyne <j@getutm.app>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  accel/tcg/translate-all.c | 65 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 1931e65365..17df6c94fa 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1166,9 +1166,71 @@ static bool alloc_code_gen_buffer_splitwx_memfd(size_t 
> size, Error **errp)
>  }
>  #endif /* CONFIG_POSIX */
>
> +#ifdef CONFIG_DARWIN
> +#include <mach/mach.h>
> +
> +extern kern_return_t mach_vm_remap(vm_map_t target_task,
> +                                   mach_vm_address_t *target_address,
> +                                   mach_vm_size_t size,
> +                                   mach_vm_offset_t mask,
> +                                   int flags,
> +                                   vm_map_t src_task,
> +                                   mach_vm_address_t src_address,
> +                                   boolean_t copy,
> +                                   vm_prot_t *cur_protection,
> +                                   vm_prot_t *max_protection,
> +                                   vm_inherit_t inheritance);
> +
> +static bool alloc_code_gen_buffer_splitwx_vmremap(size_t size, Error **errp)
> +{
> +    kern_return_t ret;
> +    mach_vm_address_t buf_rw, buf_rx;
> +    vm_prot_t cur_prot, max_prot;
> +
> +    /* Map the read-write portion via normal anon memory. */
> +    if (!alloc_code_gen_buffer_anon(size, PROT_READ | PROT_WRITE,
> +                                    MAP_PRIVATE | MAP_ANONYMOUS, errp)) {
> +        return false;
> +    }
> +
> +    buf_rw = (mach_vm_address_t)tcg_ctx->code_gen_buffer;
> +    buf_rx = 0;
> +    ret = mach_vm_remap(mach_task_self(),
> +                        &buf_rx,
> +                        size,
> +                        0,
> +                        VM_FLAGS_ANYWHERE,
> +                        mach_task_self(),
> +                        buf_rw,
> +                        false,
> +                        &cur_prot,
> +                        &max_prot,
> +                        VM_INHERIT_NONE);
> +    if (ret != KERN_SUCCESS) {
> +        /* TODO: Convert "ret" to a human readable error message. */
> +        error_setg(errp, "vm_remap for jit splitwx failed");
> +        munmap((void *)buf_rw, size);
> +        return false;
> +    }
> +
> +    if (mprotect((void *)buf_rx, size, PROT_READ | PROT_EXEC) != 0) {
> +        error_setg_errno(errp, errno, "mprotect for jit splitwx");
> +        munmap((void *)buf_rx, size);
> +        munmap((void *)buf_rw, size);
> +        return false;
> +    }
> +
> +    tcg_splitwx_diff = buf_rx - buf_rw;
> +    return true;
> +}
> +#endif /* CONFIG_DARWIN */
> +
>  static bool alloc_code_gen_buffer_splitwx(size_t size, Error **errp)
>  {
>      if (TCG_TARGET_SUPPORT_MIRROR) {
> +#ifdef CONFIG_DARWIN
> +        return alloc_code_gen_buffer_splitwx_vmremap(size, errp);
> +#endif
>  #ifdef CONFIG_POSIX
>          return alloc_code_gen_buffer_splitwx_memfd(size, errp);
>  #endif
> @@ -1201,6 +1263,9 @@ static bool alloc_code_gen_buffer(size_t size, int 
> splitwx, Error **errp)
>  #ifdef CONFIG_TCG_INTERPRETER
>      /* The tcg interpreter does not need execute permission. */
>      prot = PROT_READ | PROT_WRITE;
> +#elif defined(CONFIG_DARWIN)
> +    /* Applicable to both iOS and macOS (Apple Silicon). */
> +    flags |= MAP_JIT;
>  #endif
>
>      return alloc_code_gen_buffer_anon(size, prot, flags, errp);
> --
> 2.25.1
>