Re: [PATCH v2 14/19] RFC: accel/tcg: Support split-rwx for darwin/iOS with vm_remap

[Joelle van Dyne]

There's a compiler warning:

warning: incompatible pointer to integer conversion assigning to
'mach_vm_address_t' (aka 'unsigned long long') from 'void *'
[-Wint-conversion]
    buf_rw = tcg_ctx->code_gen_buffer;

I changed it to
    buf_rw = (mach_vm_address_t)tcg_ctx->code_gen_buffer;

Also, MAP_JIT doesn't work with the split mapping (it needs the same
entitlements that allows for RWX mapping) so I made the following
changes

@@ -1088,15 +1094,11 @@ static bool alloc_code_gen_buffer(size_t size,
int mirror, Error **errp)
     return true;
 }
 #else
-static bool alloc_code_gen_buffer_anon(size_t size, int prot, Error **errp)
+static bool alloc_code_gen_buffer_anon(size_t size, int prot, int
flags, Error **errp)
 {
-    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
     void *buf;

-#ifdef CONFIG_DARWIN
-    /* Applicable to both iOS and macOS (Apple Silicon). */
-    flags |= MAP_JIT;
-#endif
+    flags |= MAP_PRIVATE | MAP_ANONYMOUS;

     buf = mmap(NULL, size, prot, flags, -1, 0);
     if (buf == MAP_FAILED) {
@@ -1211,7 +1213,7 @@ static bool
alloc_code_gen_buffer_mirror_vmremap(size_t size, Error **errp)
     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, errp)) {
+    if (!alloc_code_gen_buffer_anon(size, PROT_READ | PROT_WRITE, 0, errp)) {
         return false;
     }

@@ -1263,6 +1265,8 @@ static bool alloc_code_gen_buffer_mirror(size_t
size, Error **errp)

 static bool alloc_code_gen_buffer(size_t size, int mirror, Error **errp)
 {
+    int flags = 0;
+
     if (mirror) {
         Error *local_err = NULL;
         if (alloc_code_gen_buffer_mirror(size, &local_err)) {
@@ -1283,8 +1287,11 @@ static bool alloc_code_gen_buffer(size_t size,
int mirror, Error **errp)
     /* The tcg interpreter does not need execute permission. */
     prot = PROT_READ | PROT_WRITE;
 #endif
+#ifdef CONFIG_DARWIN
+    flags |= MAP_JIT;
+#endif

-    return alloc_code_gen_buffer_anon(size, prot, errp);
+    return alloc_code_gen_buffer_anon(size, prot, flags, errp);
 }
 #endif /* USE_STATIC_CODE_GEN_BUFFER, WIN32, POSIX */

With this in addition to the iOS host patches, I was able to run it on
the iPad but am getting random crashes that I am continuing to debug.

-j

On Thu, Oct 29, 2020 at 5:49 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Cribbed from code posted by Joelle van Dyne <j@getutm.app>,
> and rearranged to a cleaner structure.  Completely untested.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  accel/tcg/translate-all.c | 68 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 67 insertions(+), 1 deletion(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 3e69ebd1d3..bf8263fdb4 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1093,6 +1093,11 @@ static bool alloc_code_gen_buffer_anon(size_t size, 
> int prot, Error **errp)
>      int flags = MAP_PRIVATE | MAP_ANONYMOUS;
>      void *buf;
>
> +#ifdef CONFIG_DARWIN
> +    /* Applicable to both iOS and macOS (Apple Silicon). */
> +    flags |= MAP_JIT;
> +#endif
> +
>      buf = mmap(NULL, size, prot, flags, -1, 0);
>      if (buf == MAP_FAILED) {
>          error_setg_errno(errp, errno,
> @@ -1182,13 +1187,74 @@ static bool alloc_code_gen_buffer_mirror_memfd(size_t 
> size, Error **errp)
>      qemu_madvise(buf_rx, size, QEMU_MADV_HUGEPAGE);
>      return true;
>  }
> -#endif
> +#endif /* CONFIG_LINUX */
> +
> +#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_mirror_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, errp)) {
> +        return false;
> +    }
> +
> +    buf_rw = tcg_ctx->code_gen_buffer;
> +    buf_rx = 0;
> +    ret = mach_vm_remap(mach_task_self(),
> +                        &buf_rx,
> +                        size,
> +                        0,
> +                        VM_FLAGS_ANYWHERE | VM_FLAGS_RANDOM_ADDR,
> +                        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 mirror 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 mirror");
> +        munmap((void *)buf_rx, size);
> +        munmap((void *)buf_rw, size);
> +        return false;
> +    }
> +
> +    tcg_rx_mirror_diff = buf_rx - buf_rw;
> +    return true;
> +}
> +#endif /* CONFIG_DARWIN */
>
>  static bool alloc_code_gen_buffer_mirror(size_t size, Error **errp)
>  {
>      if (TCG_TARGET_SUPPORT_MIRROR) {
>  #ifdef CONFIG_LINUX
>          return alloc_code_gen_buffer_mirror_memfd(size, errp);
> +#endif
> +#ifdef CONFIG_DARWIN
> +        return alloc_code_gen_buffer_mirror_vmremap(size, errp);
>  #endif
>      }
>      error_setg(errp, "jit split-rwx not supported");
> --
> 2.25.1
>