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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 13.01.25 10:09, Thomas Weißschuh wrote: > On Fri, Jan 10, 2025 at 04:41:03PM +0100, David Hildenbrand wrote: >> On 10.01.25 14:05, Thomas Weißschuh wrote: >>> The virtual_address_range selftest reads from the start of each mapping >>> listed in /proc/self/maps. >>> However not all mappings are valid to be arbitrarily accessed. >>> For example the vvar data used for virtual clocks on x86 [vvar_vclock] >>> can only be accessed if 1) the kernel configuration enables virtual >>> clocks and 2) the hypervisor provided the data for it. >>> Only the VDSO itself has the necessary information to know this. >>> Since commit e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping") >>> the virtual clock data was split out into its own mapping, leading >>> to EFAULT from read() during the validation. >>> >>> Skip the various vvar mappings in virtual_address_range to avoid the issue. >>> >>> Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping") >>> Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()") >>> Reported-by: kernel test robot >>> Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@intel.com >>> Signed-off-by: Thomas Weißschuh >>> --- >>> tools/testing/selftests/mm/virtual_address_range.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c >>> index 4fc1c21a5e218eaec4d059b75c31a21dd4e8a215..993990aba56fc986c42084ffa91973558aa07e87 100644 >>> --- a/tools/testing/selftests/mm/virtual_address_range.c >>> +++ b/tools/testing/selftests/mm/virtual_address_range.c >>> @@ -152,6 +152,10 @@ static int validate_complete_va_space(void) >>> if (prot[0] != 'r') >>> continue; >>> + /* Only the VDSO can know if a VVAR mapping is really readable */ >>> + if (vma_name && !strncmp(vma_name, "[vvar", 5)) >>> + continue; >> >> I'm wondering if there is a more generic way ... but likely not when staring >> at /proc/self/maps. >> >> /proc/self/smaps would indicate this as >> >> VM_IO: "io" >> VM_DONTDUMP: "dd" >> VM_PFNMAP: "pf" >> >> Especially checking for VM_IO sounds reasonable ... > > Agreed. > > Can we instead rely on madvise(MADV_DOFORK) returning EINVAL iff VM_IO? That might be one option indeed, although it feels like this is something that might change in the future ... not sure. MADV_POPULATE_READ fails with -EFAULT on VM_IO, but also on VM_PFNMAP and some other conditions, and might not be completely what we want. We do have some initial smaps parsing in vm_util.c:__check_huge(), maybe that could be factored out / reused, not sure how hard that would be to extend to return the flags. -- Cheers, David / dhildenb