On Tue, Nov 26, 2024 at 02:34:47PM +0100, Maciej Wieczor-Retman wrote:
Recent change in how get_user() handles pointers [1] has a specific case for LAM. It assigns a different bitmask that's later used to check whether a pointer comes from userland in get_user().
While currently commented out (until LASS [2] is merged into the kernel) it's worth making changes to the LAM selftest ahead of time.
Modify cpu_has_la57() so it provides current paging level information instead of the cpuid one.
Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses get_user() in its implementation. Execute the syscall with differently tagged pointers to verify that valid user pointers are passing through and invalid kernel/non-canonical pointers are not.
Also to avoid unhelpful test failures add a check in main() to skip running tests if LAM was not compiled into the kernel.
Code was tested on a Sierra Forest Xeon machine that's LAM capable. The test was ran without issues with both the LAM lines from [1] untouched and commented out. The test was also ran without issues with LAM_SUP both enabled and disabled.
4/5 level pagetables code paths were also successfully tested in Simics on a 5-level capable machine.
[1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundatio... [2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linu...
Maciej Wieczor-Retman (3): selftests/lam: Move cpu_has_la57() to use cpuinfo flag selftests/lam: Skip test if LAM is disabled selftests/lam: Test get_user() LAM pointer handling
tools/testing/selftests/x86/lam.c | 122 ++++++++++++++++++++++++++++-- 1 file changed, 117 insertions(+), 5 deletions(-)
Apart from the nitpick in 1/3, looks good to me:
Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com