Messages in this thread | | | Subject | Re: [PATCH 00/12] mm/debug_vm_pgtable: Enhancements | From | Anshuman Khandual <> | Date | Mon, 12 Jul 2021 09:44:46 +0530 |
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Hi Gavin,
Though I have not jumped into the details for all individual patches here but still have some high level questions below.
On 7/6/21 11:47 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. All these variables are first prepared in debug_vm_pgtable(), before getting passed into respective individual test functions. Also these test functions receive only the required number of variables not all. Adding a structure that captures all test parameters at once before passing them down will be unnecessary. I am still wondering what will be the real benefit of this large code churn ?
> > (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_{pud, pmd, pte}_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.
Using 'start_kernel' based method for struct page usage, enabled this test to run on platforms which might not have enough memory required for various individual test functions. This method is not a problem for tests that just need an aligned pfn (which creates a page table entry) not a real struct page.
But not allocating and owning the struct page might be problematic for tests that expect a real struct page and transform its state via set_ {pud, pmd, pte}_at() functions as reported here.
> > "struct vm_pgtable_debug" 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.
For all basic pfn requiring tests, existing 'start_kernel' based method should continue but allocate a struct page for other tests which change the passed struct page. Skipping the tests when allocation fails is the right thing to do.
- Anshuman
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