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accel/tcg: Support split-wx for linux with memfd 

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.

Reviewed-by: Joelle van Dyne <j@getutm.app>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2020-10-28 22:49:42 -07:00
parent a35b3e1415
commit a8c35b2cad
1 changed files with 76 additions and 8 deletions
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84
accel/tcg/translate-all.c
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@ -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)