Re: [PATCH v4 00/12] mm/debug_vm_pgtable: Enhancements

From: Gavin Shan
Date: Sun Aug 01 2021 - 20:13:18 EST

Hi Anshuman,

On 7/29/21 5:14 PM, Anshuman Khandual wrote:
On 7/27/21 11:43 AM, 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 access 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

* Determine the page allocation method according to
MAX_ORDER (Anshuman)
* Move existing comments to init_args() (Anshuman)
* Code refactoring as suggested by Anshuman (Anshuman)
* Improved commit log and add comments for flush_dcache_page()
in PATCH[v4 12/12] (Anshuman)
* Address misc comments (Anshuman

This series builds ok on all supported platforms but should also be tested
on them as well i.e s390, ppc, arc and riscv. I was able to do some tests
on arm64 and x86 platforms.

I had tests on the platforms except arc as it's not supported by QEMU yet.
The test is pretty simple to boot the kernel and see if there is any warning
raised from mm/debug_vm_pgtable. Everything looks good.

The test was done on v5, which will be posted pretty soon. Thanks again for
your continuous review.