On Fri, 22 Mar 2024 at 16:41, David Hildenbrand <david@xxxxxxxxxx> wrote:
> But at least the vmsplice() just seems to work. Which is weird, because
> GUP-fast should not apply (page not faulted in?)
But it is faulted in, and that indeed seems to be the root cause.
Improved repro:
#define _GNU_SOURCE
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
#include <sys/syscall.h>
int main(void)
{
int fd1, fd2;
int pip[2];
struct iovec iov;
char *addr;
int ret;
fd1 = syscall(__NR_memfd_secret, 0);
addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd1, 0);
ftruncate(fd1, 7);
addr[0] = 1; /* fault in page */
pipe(pip);
iov.iov_base = addr;
iov.iov_len = 0x50;
ret = vmsplice(pip[1], &iov, 1, 0);
if (ret == -1 && errno == EFAULT) {
printf("Success\n");
return 0;
}
fd2 = open("/tmp/repro-secretmem.test", O_RDWR | O_CREAT, 0x600);
splice(pip[0], NULL, fd2, NULL, 0x50, 0);
return 0;
}
