Re: [PATCH v3 15/41] accel/tcg: Support split-wx for linux with memfd

[Alex Bennée]

Richard Henderson <richard.henderson@linaro.org> writes:

> We cannot use a real temp file, because we would need to find
> a filesystem that does not have noexec enabled.  However, a
> memfd is not associated with any filesystem.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

It looks like this breaks --enable-tcg-interpreter:

  FAILED: libqemu-ppc64-softmmu.fa.p/accel_tcg_translate-all.c.o
  cc -Ilibqemu-ppc64-softmmu.fa.p -I. -I../.. -Itarget/ppc -I../../target/ppc 
-I../../dtc/libfdt -I../../capstone/include/capstone -Iqapi -Itrace -Iui 
-Iui/shader -I/usr/include/spice-server -I/usr/include/spice-1 
-I/usr/include/pixman-1 -I/usr/include/libdrm -I/usr/include/glib-2.0 
-I/usr/lib/x86_64-linux-gnu/glib-2.0/include -fdiagnostics-color=auto -pipe 
-Wall -Winvalid-pch -Werror -std=gnu99 -O2 -g -U_FORTIFY_SOURCE 
-D_FORTIFY_SOURCE=2 -m64 -mcx16 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 
-D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wundef 
-Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv 
-Wold-style-declaration -Wold-style-definition -Wtype-limits -Wformat-security 
-Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs 
-Wendif-labels -Wexpansion-to-defined -Wno-missing-include-dirs 
-Wno-shift-negative-value -Wno-psabi -fstack-protector-strong 
-DLEGACY_RDMA_REG_MR -isystem /home/alex/lsrc/qemu.git/linux-headers -isystem 
linux-headers -iquote /home/alex/lsrc/qemu.git/tcg/tci -iquote . -iquote 
/home/alex/lsrc/qemu.git -iquote /home/alex/lsrc/qemu.git/accel/tcg -iquote 
/home/alex/lsrc/qemu.git/include -iquote /home/alex/lsrc/qemu.git/disas/libvixl 
-pthread -fPIC -isystem../../linux-headers -isystemlinux-headers -DNEED_CPU_H 
'-DCONFIG_TARGET="ppc64-softmmu-config-target.h"' 
'-DCONFIG_DEVICES="ppc64-softmmu-config-devices.h"' -MD -MQ 
libqemu-ppc64-softmmu.fa.p/accel_tcg_translate-all.c.o -MF 
libqemu-ppc64-softmmu.fa.p/accel_tcg_translate-all.c.o.d -o 
libqemu-ppc64-softmmu.fa.p/accel_tcg_translate-all.c.o -c 
../../accel/tcg/translate-all.c
  ../../accel/tcg/translate-all.c:1138:13: error: 
‘alloc_code_gen_buffer_splitwx_memfd’ defined but not used 
[-Werror=unused-function]
   static bool alloc_code_gen_buffer_splitwx_memfd(size_t size, Error **errp)
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors


> ---
>  accel/tcg/translate-all.c | 84 +++++++++++++++++++++++++++++++++++----
>  1 file changed, 76 insertions(+), 8 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index a29cb4a42e..1931e65365 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1078,17 +1078,11 @@ static bool alloc_code_gen_buffer(size_t size, int 
> splitwx, Error **errp)
>      return true;
>  }
>  #else
> -static bool alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
> +static bool alloc_code_gen_buffer_anon(size_t size, int prot,
> +                                       int flags, Error **errp)
>  {
> -    int prot = PROT_WRITE | PROT_READ | PROT_EXEC;
> -    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
>      void *buf;
>  
> -    if (splitwx > 0) {
> -        error_setg(errp, "jit split-wx not supported");
> -        return false;
> -    }
> -
>      buf = mmap(NULL, size, prot, flags, -1, 0);
>      if (buf == MAP_FAILED) {
>          error_setg_errno(errp, errno,
> @@ -1137,6 +1131,80 @@ static bool alloc_code_gen_buffer(size_t size, int 
> splitwx, Error **errp)
>      tcg_ctx->code_gen_buffer = buf;
>      return true;
>  }
> +
> +#ifdef CONFIG_POSIX
> +#include "qemu/memfd.h"
> +
> +static bool alloc_code_gen_buffer_splitwx_memfd(size_t size, Error **errp)
> +{
> +    void *buf_rw, *buf_rx;
> +    int fd = -1;
> +
> +    buf_rw = qemu_memfd_alloc("tcg-jit", size, 0, &fd, errp);
> +    if (buf_rw == NULL) {
> +        return false;
> +    }
> +
> +    buf_rx = mmap(NULL, size, PROT_READ | PROT_EXEC, MAP_SHARED, fd, 0);
> +    if (buf_rx == MAP_FAILED) {
> +        error_setg_errno(errp, errno,
> +                         "failed to map shared memory for execute");
> +        munmap(buf_rw, size);
> +        close(fd);
> +        return false;
> +    }
> +    close(fd);
> +
> +    tcg_ctx->code_gen_buffer = buf_rw;
> +    tcg_ctx->code_gen_buffer_size = size;
> +    tcg_splitwx_diff = buf_rx - buf_rw;
> +
> +    /* Request large pages for the buffer and the splitwx.  */
> +    qemu_madvise(buf_rw, size, QEMU_MADV_HUGEPAGE);
> +    qemu_madvise(buf_rx, size, QEMU_MADV_HUGEPAGE);
> +    return true;
> +}
> +#endif /* CONFIG_POSIX */
> +
> +static bool alloc_code_gen_buffer_splitwx(size_t size, Error **errp)
> +{
> +    if (TCG_TARGET_SUPPORT_MIRROR) {
> +#ifdef CONFIG_POSIX
> +        return alloc_code_gen_buffer_splitwx_memfd(size, errp);
> +#endif
> +    }
> +    error_setg(errp, "jit split-wx not supported");
> +    return false;
> +}
> +
> +static bool alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
> +{
> +    ERRP_GUARD();
> +    int prot, flags;
> +
> +    if (splitwx) {
> +        if (alloc_code_gen_buffer_splitwx(size, errp)) {
> +            return true;
> +        }
> +        /*
> +         * If splitwx force-on (1), fail;
> +         * if splitwx default-on (-1), fall through to splitwx off.
> +         */
> +        if (splitwx > 0) {
> +            return false;
> +        }
> +        error_free_or_abort(errp);
> +    }
> +
> +    prot = PROT_READ | PROT_WRITE | PROT_EXEC;
> +    flags = MAP_PRIVATE | MAP_ANONYMOUS;
> +#ifdef CONFIG_TCG_INTERPRETER
> +    /* The tcg interpreter does not need execute permission. */
> +    prot = PROT_READ | PROT_WRITE;
> +#endif
> +
> +    return alloc_code_gen_buffer_anon(size, prot, flags, errp);
> +}
>  #endif /* USE_STATIC_CODE_GEN_BUFFER, WIN32, POSIX */
>  
>  static bool tb_cmp(const void *ap, const void *bp)


-- 
Alex Bennée