Messages in this thread | | | Subject | Re: [PATCH v2] x86/mm: fix kern_addr_valid to cope with existing but not present entries | From | Dave Hansen <> | Date | Wed, 25 Aug 2021 11:47:10 -0700 |
| |
On 8/19/21 6:27 AM, Mike Rapoport wrote: > Such PMDs are created when free_kernel_image_pages() frees regions larger > than 2Mb. In this case a part of the freed memory is mapped with PMDs and > the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will > mark the PMD as not present rather than wipe it completely. > > Make kern_addr_valid() to check whether higher level page table entries are > present before trying to dereference them to fix this issue and to avoid > similar issues in the future. > > Reported-by: Jiri Olsa <jolsa@redhat.com> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > Cc: <stable@vger.kernel.org> # 4.4... > pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > + if (!pmd_present(*pmd)) > return 0;
Yeah, that seems like the right fix. The one kern_addr_valid() user is going to touch the memory so it *better* be present. p*d_none() was definitely the wrong check.
Acked-by: Dave Hansen <dave.hansen@intel.com>
| |