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update userfaultfd handling. #228

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merged 1 commit into from
Apr 22, 2024
Merged

update userfaultfd handling. #228

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32 changes: 29 additions & 3 deletions src/iso_alloc_sanity.c
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Original file line number Diff line number Diff line change
Expand Up @@ -142,19 +142,37 @@ struct uffdio_api _uffd_api;
int64_t _uf_fd;

INTERNAL_HIDDEN void _iso_alloc_setup_userfaultfd(void) {
_uf_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
int flags = O_CLOEXEC | O_NONBLOCK;

#ifdef UFFD_USER_MODE_ONLY
/* Below, the syscall fails not necessarily because lack of kernel support.
* By default, the `unprivileged_userfaultfd` flag is disabled.
* From Linux 5.11 however, we can handle pages registered from the user-space. */
flags |= UFFD_USER_MODE_ONLY;
#endif
_uf_fd = syscall(__NR_userfaultfd, flags);

if(_uf_fd == ERR) {
LOG_AND_ABORT("This kernel does not support userfaultfd");
LOG_AND_ABORT("This kernel does not support userfaultfd or is disallowed in the user-space");
}

_uffd_api.api = UFFD_API;
_uffd_api.features = 0;

#if THREAD_SUPPORT
_uffd_api.features |= UFFD_FEATURE_THREAD_ID;
#endif

if(ioctl(_uf_fd, UFFDIO_API, &_uffd_api) == ERR) {
LOG_AND_ABORT("Failed to setup userfaultfd with ioctl");
}

#if THREAD_SUPPORT
if(!(_uffd_api.features & UFFD_FEATURE_THREAD_ID)) {
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Does the ioctl call reset this if it cannot be used?

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seems to be the case.

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Should we also check errno for -EFAULT here?

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not sure we really need to, return value is checked for ioctl already.

LOG_AND_ABORT("Failed to setup userfaultfd with thread id report");
}
#endif

if(_page_fault_thread == 0) {
int32_t s = pthread_create(&_page_fault_thread, NULL, _page_fault_thread_handler, NULL);

Expand Down Expand Up @@ -220,8 +238,12 @@ INTERNAL_HIDDEN void *_page_fault_thread_handler(void *unused) {
reg.range.len = g_page_size;
}

if((ioctl(_uf_fd, UFFDIO_UNREGISTER, &reg.range)) == ERR) {
if(UNLIKELY((ioctl(_uf_fd, UFFDIO_UNREGISTER, &reg.range)) == ERR)) {
#if THREAD_SUPPORT
LOG_AND_ABORT("Failed to unregister address %p, thread %u", umsg.arg.pagefault.address, umsg.arg.pagefault.feat.ptid);
#else
LOG_AND_ABORT("Failed to unregister address %p", umsg.arg.pagefault.address);
#endif
}

UNLOCK_SANITY_CACHE();
Expand All @@ -230,7 +252,11 @@ INTERNAL_HIDDEN void *_page_fault_thread_handler(void *unused) {

/* Detects a read of an uninitialized page */
if((umsg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE) == 0) {
#ifdef THREAD_SUPPORT
LOG_AND_ABORT("Uninitialized read detected on page %p, thread %u", umsg.arg.pagefault.address, umsg.arg.pagefault.feat.ptid);
#else
LOG_AND_ABORT("Uninitialized read detected on page %p", umsg.arg.pagefault.address);
#endif
}

UNLOCK_SANITY_CACHE();
Expand Down
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