Re: [PATCH v6 00/12] mm/debug_vm_pgtable: Enhancements

From: Gavin Shan
Date: Fri Aug 13 2021 - 05:25:39 EST

Hi Anshuman and Vineet,

On 8/12/21 9:11 PM, Anshuman Khandual wrote:
On 8/9/21 2:56 PM, Gavin Shan wrote:
There are couple of issues with current implementations and this series
tries to resolve the issues:

(a) All needed information are scattered in variables, passed to various
test functions. The code is organized in pretty much relaxed fashion.

(b) The page isn't allocated from buddy during page table entry modifying
tests. The page can be invalid, conflicting to the implementations
of set_xxx_at() on ARM64. The target page is accessed so that the
iCache can be flushed when execution permission is given on ARM64.
Besides, the target page can be unmapped and accessing to it causes
kernel crash.

"struct pgtable_debug_args" is introduced to address issue (a). For issue
(b), the used page is allocated from buddy in page table entry modifying
tests. The corresponding tets will be skipped if we fail to allocate the
(huge) page. For other test cases, the original page around to kernel
symbol (@start_kernel) is still used.

The patches are organized as below. PATCH[2-10] could be combined to one
patch, but it will make the review harder:

PATCH[1] introduces "struct pgtable_debug_args" as place holder of all
needed information. With it, the old and new implementation
can coexist.
PATCH[2-10] uses "struct pgtable_debug_args" in various test functions.
PATCH[11] removes the unused code for old implementation.
PATCH[12] fixes the issue of corrupted page flag for ARM64

* Populate saved page table entry pointers after
they're allocated in init_args() (Anshuman)
* Fix imbalanced preemption count issue by replacing
pte_alloc_mmap() with pte_alloc() in init_args() (syzbot)

+ vgupta@xxxxxxxxxx

Hello Gavin/Vineet,

This series still need to be tested on ARC ?

Yes, I'm unable to test ARC as it's not supported by QEMU yet.
It would great if Vineet can give it a try on ARC :)