[Intel-gfx] [PATCH i-g-t v2] igt/gem_userptr: Check read-only mappings
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Fri Jun 29 09:31:23 UTC 2018
On 29/06/2018 08:44, Chris Wilson wrote:
> Setup a userptr object that only has a read-only mapping back to a file
> store (memfd). Then attempt to write into that mapping using the GPU and
> assert that those writes do not land (while also writing via a writable
> userptr mapping into the same memfd to verify that the GPU is working!)
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
> Minor commentary additions
> ---
> configure.ac | 1 +
> lib/ioctl_wrappers.c | 4 +-
> lib/ioctl_wrappers.h | 4 +-
> lib/meson.build | 1 +
> meson.build | 1 +
> tests/Makefile.am | 4 +-
> tests/gem_userptr_blits.c | 372 +++++++++++++++++++++++++++++++++++++-
> 7 files changed, 377 insertions(+), 10 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index 1ee4e90e9..195963d4f 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -125,6 +125,7 @@ PKG_CHECK_MODULES(PCIACCESS, [pciaccess >= 0.10])
> PKG_CHECK_MODULES(KMOD, [libkmod])
> PKG_CHECK_MODULES(PROCPS, [libprocps])
> PKG_CHECK_MODULES(LIBUNWIND, [libunwind])
> +PKG_CHECK_MODULES(SSL, [openssl])
> PKG_CHECK_MODULES(VALGRIND, [valgrind], [have_valgrind=yes], [have_valgrind=no])
>
> if test x$have_valgrind = xyes; then
> diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
> index 79db44a8c..d5d2a4e4c 100644
> --- a/lib/ioctl_wrappers.c
> +++ b/lib/ioctl_wrappers.c
> @@ -869,7 +869,7 @@ int gem_madvise(int fd, uint32_t handle, int state)
> return madv.retained;
> }
>
> -int __gem_userptr(int fd, void *ptr, int size, int read_only, uint32_t flags, uint32_t *handle)
> +int __gem_userptr(int fd, void *ptr, uint64_t size, int read_only, uint32_t flags, uint32_t *handle)
> {
> struct drm_i915_gem_userptr userptr;
>
> @@ -898,7 +898,7 @@ int __gem_userptr(int fd, void *ptr, int size, int read_only, uint32_t flags, ui
> *
> * Returns userptr handle for the GEM object.
> */
> -void gem_userptr(int fd, void *ptr, int size, int read_only, uint32_t flags, uint32_t *handle)
> +void gem_userptr(int fd, void *ptr, uint64_t size, int read_only, uint32_t flags, uint32_t *handle)
> {
> igt_assert_eq(__gem_userptr(fd, ptr, size, read_only, flags, handle), 0);
> }
> diff --git a/lib/ioctl_wrappers.h b/lib/ioctl_wrappers.h
> index b966f72c9..8e2cd380b 100644
> --- a/lib/ioctl_wrappers.h
> +++ b/lib/ioctl_wrappers.h
> @@ -133,8 +133,8 @@ struct local_i915_gem_userptr {
> #define LOCAL_I915_USERPTR_UNSYNCHRONIZED (1<<31)
> uint32_t handle;
> };
> -void gem_userptr(int fd, void *ptr, int size, int read_only, uint32_t flags, uint32_t *handle);
> -int __gem_userptr(int fd, void *ptr, int size, int read_only, uint32_t flags, uint32_t *handle);
> +void gem_userptr(int fd, void *ptr, uint64_t size, int read_only, uint32_t flags, uint32_t *handle);
> +int __gem_userptr(int fd, void *ptr, uint64_t size, int read_only, uint32_t flags, uint32_t *handle);
>
> void gem_sw_finish(int fd, uint32_t handle);
>
> diff --git a/lib/meson.build b/lib/meson.build
> index 1a355414e..939167f91 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -62,6 +62,7 @@ lib_deps = [
> pthreads,
> math,
> realtime,
> + ssl,
> ]
>
> if libdrm_intel.found()
> diff --git a/meson.build b/meson.build
> index 4d15d6238..638c01066 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -98,6 +98,7 @@ pciaccess = dependency('pciaccess', version : '>=0.10')
> libkmod = dependency('libkmod')
> libprocps = dependency('libprocps', required : true)
> libunwind = dependency('libunwind', required : true)
> +ssl = dependency('openssl', required : true)
>
> valgrind = null_dep
> valgrindinfo = 'No'
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index f41ad5096..ba307b220 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -126,8 +126,8 @@ gem_tiled_swapping_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> gem_tiled_swapping_LDADD = $(LDADD) -lpthread
> prime_self_import_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> prime_self_import_LDADD = $(LDADD) -lpthread
> -gem_userptr_blits_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> -gem_userptr_blits_LDADD = $(LDADD) -lpthread
> +gem_userptr_blits_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS) $(SSL_CFLAGS)
> +gem_userptr_blits_LDADD = $(LDADD) $(SSL_LIBS) -lpthread
> perf_pmu_LDADD = $(LDADD) $(top_builddir)/lib/libigt_perf.la
>
> gem_eio_LDADD = $(LDADD) -lrt
> diff --git a/tests/gem_userptr_blits.c b/tests/gem_userptr_blits.c
> index 7e3b6ef38..0fb7eba04 100644
> --- a/tests/gem_userptr_blits.c
> +++ b/tests/gem_userptr_blits.c
> @@ -43,13 +43,17 @@
> #include <fcntl.h>
> #include <inttypes.h>
> #include <errno.h>
> +#include <setjmp.h>
> #include <sys/stat.h>
> #include <sys/time.h>
> #include <sys/mman.h>
> +#include <openssl/sha.h>
> #include <signal.h>
> #include <pthread.h>
> #include <time.h>
>
> +#include <linux/memfd.h>
> +
> #include "drm.h"
> #include "i915_drm.h"
>
> @@ -238,6 +242,57 @@ blit(int fd, uint32_t dst, uint32_t src, uint32_t *all_bo, int n_bo)
> return ret;
> }
>
> +static void store_dword(int fd, uint32_t target,
> + uint32_t offset, uint32_t value)
> +{
> + const int gen = intel_gen(intel_get_drm_devid(fd));
> + struct drm_i915_gem_exec_object2 obj[2];
> + struct drm_i915_gem_relocation_entry reloc;
> + struct drm_i915_gem_execbuffer2 execbuf;
> + uint32_t batch[16];
> + int i;
> +
> + memset(&execbuf, 0, sizeof(execbuf));
> + execbuf.buffers_ptr = to_user_pointer(obj);
> + execbuf.buffer_count = ARRAY_SIZE(obj);
> + execbuf.flags = 0;
> + if (gen < 6)
> + execbuf.flags |= I915_EXEC_SECURE;
> +
> + memset(obj, 0, sizeof(obj));
> + obj[0].handle = target;
> + obj[1].handle = gem_create(fd, 4096);
> +
> + memset(&reloc, 0, sizeof(reloc));
> + reloc.target_handle = obj[0].handle;
> + reloc.presumed_offset = 0;
> + reloc.offset = sizeof(uint32_t);
> + reloc.delta = offset;
> + reloc.read_domains = I915_GEM_DOMAIN_RENDER;
> + reloc.write_domain = I915_GEM_DOMAIN_RENDER;
> + obj[1].relocs_ptr = to_user_pointer(&reloc);
> + obj[1].relocation_count = 1;
> +
> + i = 0;
> + batch[i] = MI_STORE_DWORD_IMM | (gen < 6 ? 1 << 22 : 0);
> + if (gen >= 8) {
> + batch[++i] = offset;
> + batch[++i] = 0;
> + } else if (gen >= 4) {
> + batch[++i] = 0;
> + batch[++i] = offset;
> + reloc.offset += sizeof(uint32_t);
> + } else {
> + batch[i]--;
> + batch[++i] = offset;
> + } > + batch[++i] = value;
I still think to avoid too much code duplication:
batch = __emit_store_dword(batch, gen, offset, value, &reloc.offset)
Then from there see if something more could be extracted form the three
call sites.
> + batch[++i] = MI_BATCH_BUFFER_END;
> + gem_write(fd, obj[1].handle, 0, batch, sizeof(batch));
> + gem_execbuf(fd, &execbuf);
> + gem_close(fd, obj[1].handle);
> +}
> +
> static uint32_t
> create_userptr(int fd, uint32_t val, uint32_t *ptr)
> {
> @@ -941,6 +996,310 @@ static int test_dmabuf(void)
> return 0;
> }
>
> +static void test_readonly(int i915)
> +{
> + unsigned char orig[SHA_DIGEST_LENGTH];
> + uint64_t aperture_size;
> + uint32_t whandle, rhandle;
> + size_t sz, total;
> + void *pages, *space;
> + int memfd;
> +
> + /*
> + * A small batch of pages; small enough to cheaply check for stray
> + * writes but large enough that we don't create too many VMA pointing
> + * back to this set from the large arena. The limit on total number
> + * of VMA for a process is 65,536 (at least on this kernel).
> + *
> + * We then write from the GPU through the large arena into the smaller
> + * backing storage, which we can cheaply check to see if those writes
> + * have landed (using a SHA1sum). Repeating the same random GPU writes
> + * though a read-only handle to confirm that this time the writes are
through
> + * discarded and the backing store unchanged.
> + */
> + sz = 16 << 12;
Here you aim not to exceed the above mentioned per-process VMA limit but
please just express that in the code. Maybe re-order the code a bit:
total = 2Gib
sz = 2Gib / max_vmas_per_process * 2
aperture_size = ...
total = round_down
Then proceed with allocation etc.
> + memfd = memfd_create("pages", 0);
> + igt_require(memfd != -1);
> + igt_require(ftruncate(memfd, sz) == 0);
> +
> + pages = mmap(NULL, sz, PROT_WRITE, MAP_SHARED, memfd, 0);
> + igt_assert(pages != MAP_FAILED);
> +
> + igt_require(__gem_userptr(i915, pages, sz, true, userptr_flags, &rhandle) == 0);
> + gem_close(i915, rhandle);
> +
> + gem_userptr(i915, pages, sz, false, userptr_flags, &whandle);
> +
/*
From your reply:
"""
the largest offset we can use is 4G, and we can't use the full range
as we need some extra room for batches, and we can't use the full VMA
limit without serious slow down and risk of exhaustion.
Then sticking to a pot.
"""
*/
> + total = 2048ull << 20;
> + aperture_size = gem_aperture_size(i915) / 2;
> + if (aperture_size < total)
> + total = aperture_size;
> + total = total / sz * sz;
> + igt_info("Using a %'zuB (%'zu pages) arena onto %zu pages\n",
> + total, total >> 12, sz >> 12);
> +
> + /* Create an arena all pointing to the same set of pages */
> + space = mmap(NULL, total, PROT_READ, MAP_ANON | MAP_SHARED, -1, 0);
Why MAP_SHARED?
> + igt_require(space != MAP_FAILED);
> + for (size_t offset = 0; offset < total; offset += sz) {
> + igt_assert(mmap(space + offset, sz,
> + PROT_WRITE, MAP_SHARED | MAP_FIXED,
> + memfd, 0) != MAP_FAILED);
> + *(uint32_t *)(space + offset) = offset;
AFAIU:
First write instantiates the backing store, well, one page of it I
guess. Depending how memfd works I guess. But mlock later will do all of it.
> + }
> + igt_assert_eq_u32(*(uint32_t *)pages, (uint32_t)(total - sz));
... and this checks that the arena is made up from repeating chunks.
(Checking that the signature written into the last chunk is mirrored in
the first one.)
> + igt_assert(mlock(space, total) == 0);
So this allocates all 64KiB definitely.
> + close(memfd);
> +
> + /* Check we can create a normal userptr bo wrapping the wrapper */
> + gem_userptr(i915, space, total, false, userptr_flags, &rhandle);
This is not read-only so rhandle is a bit misleading. Why do you btw
create the whandle so early on and not just here? Hmm... whandle is
chunk size, rhandle is arena size.. so the two loops below are different
in that respect. Why is that?
> + gem_set_domain(i915, rhandle, I915_GEM_DOMAIN_CPU, 0);
> + for (size_t offset = 0; offset < total; offset += sz)
> + store_dword(i915, rhandle, offset + 4, offset / sz);
> + gem_sync(i915, rhandle);
I did not get your last reply here - once store dwords have completed
and you proceed to check the memory via CPU PTEs - do you need to move
the userptr bo back to the CPU domain so any flushes would happen?
> + igt_assert_eq_u32(*(uint32_t *)(pages + 0), (uint32_t)(total - sz));
> + igt_assert_eq_u32(*(uint32_t *)(pages + 4), (uint32_t)(total / sz - 1));
I really think comment explaining the layout and which side writes at
which offset would be beneficial.
> + gem_close(i915, rhandle);
> +
> + /* Now enforce read-only henceforth */
> + igt_assert(mprotect(space, total, PROT_READ) == 0);
> +
> + SHA1(pages, sz, orig);
> + igt_fork(child, 1) {
> + const int gen = intel_gen(intel_get_drm_devid(i915));
> + const int nreloc = 1024;
> + struct drm_i915_gem_relocation_entry *reloc;
> + struct drm_i915_gem_exec_object2 obj[2];
> + struct drm_i915_gem_execbuffer2 exec;
> + unsigned char ref[SHA_DIGEST_LENGTH], result[SHA_DIGEST_LENGTH];
> + uint32_t *batch;
> + int i;
> +
> + reloc = calloc(sizeof(*reloc), nreloc);
> + gem_userptr(i915, space, total, true, userptr_flags, &rhandle);
> +
> + memset(obj, 0, sizeof(obj));
> + obj[0].flags = LOCAL_EXEC_OBJECT_SUPPORTS_48B;
> + obj[1].handle = gem_create(i915, sz);
I didn't get your previous reply. This is the batch buffer right? So the
size needed is relating to the number of store dword + bbend you need to
emit, rather than sz, no? And nreloc is arbitrary subset of sz /
sizeof(uint32_t), right?
So maybe:
const int nreloc = sz / sizeof(uint32_t) / 16; /* arbitrary sub-size */
...
obj[1].handle = gem_create(i915, sizeof(uint32_t) + nreloc *
sizeof(one_store_dword_sz));
Or I am missing something?
> + obj[1].relocation_count = nreloc;
> + obj[1].relocs_ptr = to_user_pointer(reloc);
> +
> + batch = gem_mmap__wc(i915, obj[1].handle, 0, sz, PROT_WRITE);
> +
> + memset(&exec, 0, sizeof(exec));
> + exec.buffer_count = 2;
> + exec.buffers_ptr = to_user_pointer(obj);
> + if (gen < 6)
> + exec.flags |= I915_EXEC_SECURE;
> +
> + for_each_engine(i915, exec.flags) {
> + /* First tweak the backing store through the write */
> + i = 0;
> + obj[0].handle = whandle;
> + for (int n = 0; n < nreloc; n++) {
> + uint64_t offset;
> +
> + reloc[n].target_handle = obj[0].handle;
> + reloc[n].delta = rand() % (sz / 4) * 4;
> + reloc[n].offset = (i + 1) * sizeof(uint32_t);
> + reloc[n].presumed_offset = obj[0].offset;
> + reloc[n].read_domains = I915_GEM_DOMAIN_RENDER;
> + reloc[n].write_domain = I915_GEM_DOMAIN_RENDER;
How about:
__fill_reloc(&reloc, &obj[0], delta, offset) ?
> +
> + offset = reloc[n].presumed_offset + reloc[n].delta;
> +
> + batch[i] = MI_STORE_DWORD_IMM | (gen < 6 ? 1 << 22 : 0);
> + if (gen >= 8) {
> + batch[++i] = offset;
> + batch[++i] = offset >> 32;
> + } else if (gen >= 4) {
> + batch[++i] = 0;
> + batch[++i] = offset;
> + reloc[n].offset += sizeof(uint32_t);
> + } else {
> + batch[i]--;
> + batch[++i] = offset;
> + }
> + batch[++i] = rand();
> + i++;
> + }
> + batch[i] = MI_BATCH_BUFFER_END;
> + igt_assert(i * sizeof(uint32_t) < sz);
> +
> + gem_execbuf(i915, &exec);
> + gem_sync(i915, obj[0].handle);
> + SHA1(pages, sz, ref);
> +
> + igt_assert(memcmp(ref, orig, sizeof(ref)));
> + memcpy(orig, ref, sizeof(orig));
> +
> + /* Now try the same through the read-only handle */
> + i = 0;
> + obj[0].handle = rhandle;
> + for (int n = 0; n < nreloc; n++) {
> + uint64_t offset;
> +
> + reloc[n].target_handle = obj[0].handle;
> + reloc[n].delta = rand() % (total / 4) * 4;
> + reloc[n].offset = (i + 1) * sizeof(uint32_t);
> + reloc[n].presumed_offset = obj[0].offset;
> + reloc[n].read_domains = I915_GEM_DOMAIN_RENDER;
> + reloc[n].write_domain = I915_GEM_DOMAIN_RENDER;
> +
> + offset = reloc[n].presumed_offset + reloc[n].delta;
> +
> + batch[i] = MI_STORE_DWORD_IMM | (gen < 6 ? 1 << 22 : 0);
> + if (gen >= 8) {
> + batch[++i] = offset;
> + batch[++i] = offset >> 32;
> + } else if (gen >= 4) {
> + batch[++i] = 0;
> + batch[++i] = offset;
> + reloc[n].offset += sizeof(uint32_t);
> + } else {
> + batch[i]--;
> + batch[++i] = offset;
> + }
> + batch[++i] = rand();
> + i++;
> + }
> + batch[i] = MI_BATCH_BUFFER_END;
> +
> + gem_execbuf(i915, &exec);
> + gem_sync(i915, obj[0].handle);
> + SHA1(pages, sz, result);
> +
> + /*
> + * As the writes into the read-only GPU bo should fail,
> + * the SHA1 hash of the backing store should be
> + * unaffected.
> + */
> + igt_assert(memcmp(ref, result, SHA_DIGEST_LENGTH) == 0);
> + }
> +
> + munmap(batch, sz);
> + gem_close(i915, obj[1].handle);
> + gem_close(i915, rhandle);
> + }
> + igt_waitchildren();
> +
> + munmap(space, total);
> + munmap(pages, sz);
> +}
> +
> +static jmp_buf sigjmp;
> +static void sigjmp_handler(int sig)
> +{
> + siglongjmp(sigjmp, sig);
> +}
> +
> +static void test_readonly_mmap(int i915)
> +{
> + unsigned char original[SHA_DIGEST_LENGTH];
> + unsigned char result[SHA_DIGEST_LENGTH];
> + uint32_t handle;
> + uint32_t sz;
> + void *pages;
> + void *ptr;
> + int sig;
> +
> + /*
> + * A quick check to ensure that we cannot circumvent the
> + * read-only nature of our memory by creating a GTT mmap into
> + * the pages. Imagine receiving a readonly SHM segment from
> + * another process, or a readonly file mmap, it must remain readonly
> + * on the GPU as well.
> + */
> +
> + igt_require(igt_setup_clflush());
> +
> + sz = 16 << 12;
> + pages = mmap(NULL, sz, PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
> + igt_assert(pages != MAP_FAILED);
> +
> + igt_require(__gem_userptr(i915, pages, sz, true, userptr_flags, &handle) == 0);
> + gem_set_caching(i915, handle, 0);
> +
> + memset(pages, 0xa5, sz);
> + igt_clflush_range(pages, sz);
Please add comment saying why it is needed.
> + SHA1(pages, sz, original);
> +
> + ptr = __gem_mmap__gtt(i915, handle, sz, PROT_WRITE);
> + igt_assert(ptr == NULL);
> +
> + ptr = gem_mmap__gtt(i915, handle, sz, PROT_READ);
> + gem_close(i915, handle);
> +
> + /* Check that a write into the GTT readonly map fails */
> + if (!(sig = sigsetjmp(sigjmp, 1))) {
> + signal(SIGBUS, sigjmp_handler);
> + signal(SIGSEGV, sigjmp_handler);
> + memset(ptr, 0x5a, sz);
> + igt_assert(0);
> + }
> + igt_assert_eq(sig, SIGSEGV);
> +
> + /* Check that we disallow removing the readonly protection */
> + igt_assert(mprotect(ptr, sz, PROT_WRITE));
> + if (!(sig = sigsetjmp(sigjmp, 1))) {
Continuing from previous reply - there is no longjmp so I don't know who
will jump here. Maybe it is just me since I am not familiar with the
facility but I still have a feeling comment on high level setup here is
warranted.
Regards,
Tvrtko
> + signal(SIGBUS, sigjmp_handler);
> + signal(SIGSEGV, sigjmp_handler);
> + memset(ptr, 0x5a, sz);
> + igt_assert(0);
> + }
> + igt_assert_eq(sig, SIGSEGV);
> +
> + /* A single read from the GTT pointer to prove that works */
> + igt_assert_eq_u32(*(uint8_t *)ptr, 0xa5);
> + munmap(ptr, sz);
> +
> + /* Double check that the kernel did indeed not let any writes through */
> + igt_clflush_range(pages, sz);
> + SHA1(pages, sz, result);
> + igt_assert(!memcmp(original, result, sizeof(original)));
> +
> + munmap(pages, sz);
> +}
> +
> +static void test_readonly_pwrite(int i915)
> +{
> + unsigned char original[SHA_DIGEST_LENGTH];
> + unsigned char result[SHA_DIGEST_LENGTH];
> + uint32_t handle;
> + uint32_t sz;
> + void *pages;
> +
> + /*
> + * Same as for GTT mmapings, we cannot alone ourselves to
> + * circumvent readonly protection on a piece of memory via the
> + * pwrite ioctl.
> + */
> +
> + igt_require(igt_setup_clflush());
> +
> + sz = 16 << 12;
> + pages = mmap(NULL, sz, PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
> + igt_assert(pages != MAP_FAILED);
> +
> + igt_require(__gem_userptr(i915, pages, sz, true, userptr_flags, &handle) == 0);
> + memset(pages, 0xa5, sz);
> + SHA1(pages, sz, original);
> +
> + for (int page = 0; page < 16; page++) {
> + char data[4096];
> +
> + memset(data, page, sizeof(data));
> + igt_assert_eq(__gem_write(i915, handle, page << 12, data, sizeof(data)), -EINVAL);
> + }
> +
> + gem_close(i915, handle);
> +
> + SHA1(pages, sz, result);
> + igt_assert(!memcmp(original, result, sizeof(original)));
> +
> + munmap(pages, sz);
> +}
> +
> static int test_usage_restrictions(int fd)
> {
> void *ptr;
> @@ -961,10 +1320,6 @@ static int test_usage_restrictions(int fd)
> ret = __gem_userptr(fd, (char *)ptr + 1, PAGE_SIZE - 1, 0, userptr_flags, &handle);
> igt_assert_neq(ret, 0);
>
> - /* Read-only not supported. */
> - ret = __gem_userptr(fd, (char *)ptr, PAGE_SIZE, 1, userptr_flags, &handle);
> - igt_assert_neq(ret, 0);
> -
> free(ptr);
>
> return 0;
> @@ -1502,6 +1857,15 @@ int main(int argc, char **argv)
> igt_subtest("dmabuf-unsync")
> test_dmabuf();
>
> + igt_subtest("readonly-unsync")
> + test_readonly(fd);
> +
> + igt_subtest("readonly-mmap-unsync")
> + test_readonly_mmap(fd);
> +
> + igt_subtest("readonly-pwrite-unsync")
> + test_readonly_pwrite(fd);
> +
> for (unsigned flags = 0; flags < ALL_FORKING_EVICTIONS + 1; flags++) {
> igt_subtest_f("forked-unsync%s%s%s-%s",
> flags & FORKING_EVICTIONS_SWAPPING ? "-swapping" : "",
>
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