On 7/21/21 3:50 PM, Gavin Shan wrote:
> Hi Anshuman,
>
> On 7/21/21 3:44 PM, Anshuman Khandual wrote:
>> On 7/19/21 6:36 PM, Gavin Shan wrote:
>>> In debug_vm_pgtable(), there are many local variables introduced to
>>> track the needed information and they are passed to the functions for
>>> various test cases. It'd better to introduce a struct as place holder
>>> for these information. With it, what the functions for various test
>>> cases need is the struct, to simplify the code. It also makes code
>>> easier to be maintained.
>>>
>>> Besides, set_xxx_at() could access the data on the corresponding pages
>>> in the page table modifying tests. So the accessed pages in the tests
>>> should have been allocated from buddy. Otherwise, we're accessing pages
>>> that aren't owned by us. This causes issues like page flag corruption.
>>>
>>> This introduces "struct pgtable_debug_args". The struct is initialized
>>> and destroyed, but the information in the struct isn't used yet. They
>>> will be used in subsequent patches.
>>>
>>> Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
>>> ---
>>> mm/debug_vm_pgtable.c | 197 +++++++++++++++++++++++++++++++++++++++++-
>>> 1 file changed, 196 insertions(+), 1 deletion(-)
>>>
>
> I saw you've finished the review on PATCH[v3 01/12] and PATCH[v3 02/12].
> I will wait to integrate your comments to v4 until you finish the review
> on all patches in v3 series.
>
>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>> index 1c922691aa61..ea153ff40d23 100644
>>> --- a/mm/debug_vm_pgtable.c
>>> +++ b/mm/debug_vm_pgtable.c
>>> @@ -58,6 +58,36 @@
>>> #define RANDOM_ORVALUE (GENMASK(BITS_PER_LONG - 1, 0) & ~ARCH_SKIP_MASK)
>>> #define RANDOM_NZVALUE GENMASK(7, 0)
>>> +struct pgtable_debug_args {
>>> + struct mm_struct *mm;
>>> + struct vm_area_struct *vma;
>>> +
>>> + pgd_t *pgdp;
>>> + p4d_t *p4dp;
>>> + pud_t *pudp;
>>> + pmd_t *pmdp;
>>> + pte_t *ptep;
>>> +
>>> + p4d_t *start_p4dp;
>>> + pud_t *start_pudp;
>>> + pmd_t *start_pmdp;
>>> + pgtable_t start_ptep;
>>> +
>>> + unsigned long vaddr;
>>> + pgprot_t page_prot;
>>> + pgprot_t page_prot_none;
>>> +
>>> + unsigned long pud_pfn;
>>> + unsigned long pmd_pfn;
>>> + unsigned long pte_pfn;
>>> +
>>> + unsigned long fixed_pgd_pfn;
>>> + unsigned long fixed_p4d_pfn;
>>> + unsigned long fixed_pud_pfn;
>>> + unsigned long fixed_pmd_pfn;
>>> + unsigned long fixed_pte_pfn;
>>> +};
>>> +
>>> static void __init pte_basic_tests(unsigned long pfn, int idx)
>>> {
>>> pgprot_t prot = protection_map[idx];
>>> @@ -955,8 +985,167 @@ static unsigned long __init get_random_vaddr(void)
>>> return random_vaddr;
>>> }
>>> +static void __init destroy_args(struct pgtable_debug_args *args)
>>> +{
>>> + struct page *page = NULL;
>>> +
>>> + /* Free (huge) page */
>>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>>> + IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
>>> + has_transparent_hugepage() &&
>>> + args->pud_pfn != ULONG_MAX) {
>>> + page = pfn_to_page(args->pud_pfn);
>>> + __free_pages(page, HPAGE_PUD_SHIFT - PAGE_SHIFT);
>>> + } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>>> + has_transparent_hugepage() &&
>>> + args->pmd_pfn != ULONG_MAX) {
>>> + page = pfn_to_page(args->pmd_pfn);
>>> + __free_pages(page, HPAGE_PMD_ORDER);
>>> + } else if (args->pte_pfn != ULONG_MAX) {
>>> + page = pfn_to_page(args->pte_pfn);
>>> + __free_pages(page, 0);
>>> + }
>>> +
>>> + /* Free page table */
>>> + if (args->start_ptep) {
>>> + pte_free(args->mm, args->start_ptep);
>>> + mm_dec_nr_ptes(args->mm);
>>> + }
>>> +
>>> + if (args->start_pmdp) {
>>> + pmd_free(args->mm, args->start_pmdp);
>>> + mm_dec_nr_pmds(args->mm);
>>> + }
>>> +
>>> + if (args->start_pudp) {
>>> + pud_free(args->mm, args->start_pudp);
>>> + mm_dec_nr_puds(args->mm);
>>> + }
>>> +
>>> + if (args->start_p4dp)
>>> + p4d_free(args->mm, args->p4dp);
>>> +
>>> + /* Free vma and mm struct */
>>> + if (args->vma)
>>> + vm_area_free(args->vma);
>>> + if (args->mm)
>>> + mmdrop(args->mm);
>>> +}
>>> +
>>> +static int __init init_args(struct pgtable_debug_args *args)
>>> +{
>>> + struct page *page = NULL;
>>> + phys_addr_t phys;
>>> + int ret = 0;
>>> +
>>> + /* Initialize the debugging data */
>>> + memset(args, 0, sizeof(*args));
>>> + args->page_prot = vm_get_page_prot(VMFLAGS);
>>> + args->page_prot_none = __P000;
>>
>> Please preserve the existing comments before this assignment.
>>
>> /*
>> * __P000 (or even __S000) will help create page table entries with
>> * PROT_NONE permission as required for pxx_protnone_tests().
>> */
>>
>
> Sure. I will combine the comments in v4 as below:
>
> /*
> * Initialize the debugging arguments.
> *
> * __P000 (or even __S000) will help create page table entries with
> * PROT_NONE permission as required for pxx_protnone_tests().
> */
>
>
>>> + args->pud_pfn = ULONG_MAX;
>>> + args->pmd_pfn = ULONG_MAX;
>>> + args->pte_pfn = ULONG_MAX;
>>> + args->fixed_pgd_pfn = ULONG_MAX;
>>> + args->fixed_p4d_pfn = ULONG_MAX;
>>> + args->fixed_pud_pfn = ULONG_MAX;
>>> + args->fixed_pmd_pfn = ULONG_MAX;
>>> + args->fixed_pte_pfn = ULONG_MAX;
>>> +
>>> + /* Allocate mm and vma */
>>> + args->mm = mm_alloc();
>>> + if (!args->mm) {
>>> + pr_err("Failed to allocate mm struct\n");
>>> + ret = -ENOMEM;
>>> + goto error;
>>> + }
>>> +
>>> + args->vma = vm_area_alloc(args->mm);
>>> + if (!args->vma) {
>>> + pr_err("Failed to allocate vma\n");
>>> + ret = -ENOMEM;
>>> + goto error;
>>> + }
>>> +
>>> + /* Figure out the virtual address and allocate page table entries */
>>> + args->vaddr = get_random_vaddr();
>>
>> Please group args->vaddr's init with page_prot and page_prot_none above.
>>
>
> Yes, It will make the code tidy. I'll move this line accordingly in v4,
> but the related comments will be dropped as the code is self-explanatory.
>
> /* Allocate page table entries */
>
>>> + args->pgdp = pgd_offset(args->mm, args->vaddr);
>>> + args->p4dp = p4d_alloc(args->mm, args->pgdp, args->vaddr);
>>> + args->pudp = args->p4dp ?
>>> + pud_alloc(args->mm, args->p4dp, args->vaddr) : NULL;
>>> + args->pmdp = args->pudp ?
>>> + pmd_alloc(args->mm, args->pudp, args->vaddr) : NULL;
>>> + args->ptep = args->pmdp ?
>>> + pte_alloc_map(args->mm, args->pmdp, args->vaddr) : NULL;
>>> + if (!args->ptep) {
>>> + pr_err("Failed to allocate page table\n");
>>> + ret = -ENOMEM;
>>> + goto error;
>>> + }
>>
>> Why not just assert that all page table level pointers are allocated
>> successfully, otherwise bail out the test completely. Something like
>> this at each level.
>>
>> if (!args->p4dp) {
>> pr_err("Failed to allocate page table\n");
>> ret = -ENOMEM;
>> goto error;
>> }
>>
>> Is there any value in proceeding with the test when some page table
>> pointers have not been allocated. Also individual tests do not cross
>> check these pointers. Also asserting successful allocations will
>> make the freeing path simpler, as I had mentioned earlier.
>>
>
> There is no tests will be carried out if we fail to allocate any level
> of page table entries. For other questions, please refer below response.
> In summary, this snippet needs to be combined with next snippet, as below.
>
>>> +
>>> + /*
>>> + * The above page table entries will be modified. Lets save the
>>> + * page table entries so that they can be released when the tests
>>> + * are completed.
>>> + */
>>> + args->start_p4dp = p4d_offset(args->pgdp, 0UL);
>>> + args->start_pudp = pud_offset(args->p4dp, 0UL);
>>> + args->start_pmdp = pmd_offset(args->pudp, 0UL);
>>> + args->start_ptep = pmd_pgtable(READ_ONCE(*(args->pmdp)));
>>
>> If the above page table pointers have been validated to be allocated
>> successfully, we could add these here.
>>
>> WARN_ON(!args->start_p4dp)
>> WARN_ON(!args->start_pudp)
>> WARN_ON(!args->start_pmdp)
>> WARN_ON(!args->start_ptep)
>>
>> Afterwards all those if (args->start_pxdp) checks in the freeing path
>> will not be required anymore.
>>
>
> The check on @args->start_pxdp is still needed in destroy_args() for
> couple of cases: (1) destroy_args() is called on failing to allocate
> @args->mm or @args->vma. That time, no page table entries are allocated.
> (2) It's possible to fail allocating current level of page table entries
> even the previous levels of page table entries are allocated successfully.
This makes sense as destroy_args() is getting called if any of these
allocations fails during init_args(). Did not realize that earlier.
>
> So Lets change these (above) two snippets as below in v4:
>
> /*
> * Allocate page table entries. The allocated page table entries
> * will be modified in the tests. Lets save the page table entries
> * so that they can be released when the tests are completed.
> */
> args->pgdp = pgd_offset(args->mm, args->vaddr);
> args->p4dp = p4d_alloc(args->mm, args->pgdp, args->vaddr);
> if (!args->p4dp) {
> pr_err("Failed to allocate p4d entries\n");
> ret = -ENOMEM;
> goto error;
> }
>
> args->start_p4dp = p4d_offset(args->pgdp, 0UL);
Dont bring the arg->start_pxdp assignments here. If all page table level
pointer allocations succeed, they all get assigned together like we have
right now. Although a sanity check afterwards like the following, might
still be better.
WARN_ON(!args->start_p4dp)
WARN_ON(!args->start_pudp)
WARN_ON(!args->start_pmdp)
WARN_ON(!args->start_ptep)
> args->pudp = pud_alloc(args->mm, args->p4dp, args->vaddr);
> if (!args->pudp) {
> pr_err("Failed to allocate pud entries\n");
> ret = -ENOMEM;
> goto error;
> }
>
> args->pmdp = pmd_alloc(args->mm, args->pudp, args->vaddr);
> if (!args->pmdp) {
> pr_err("Failed to allocate PMD entries\n");
> ret = -ENOMEM;
> goto error;
> }
>
> args->start_pmdp = pmd_offset(args->pudp, 0UL);
> args->ptep = pte_alloc_map(args->mm, args->pmdp, args->vaddr);
> if (!args->ptep) {
> pr_err("Failed to allocate page table\n");
> ret = -ENOMEM;
> goto error;
> }
>
> args->start_ptep = pmd_pgtable(READ_ONCE(*(args->pmdp)));
>
>>> +
>>> + /*
>>> + * Figure out the fixed addresses, which are all around the kernel
>>> + * symbol (@start_kernel). The corresponding PFNs might be invalid,
>>> + * but it's fine as the following tests won't access the pages.
>>> + */
>>> + phys = __pa_symbol(&start_kernel);
>>> + args->fixed_pgd_pfn = __phys_to_pfn(phys & PGDIR_MASK);
>>> + args->fixed_p4d_pfn = __phys_to_pfn(phys & P4D_MASK);
>>> + args->fixed_pud_pfn = __phys_to_pfn(phys & PUD_MASK);
>>> + args->fixed_pmd_pfn = __phys_to_pfn(phys & PMD_MASK);
>>> + args->fixed_pte_pfn = __phys_to_pfn(phys & PAGE_MASK);
>>> +
>>> + /*
>>> + * Allocate (huge) pages because some of the tests need to access
>>> + * the data in the pages. The corresponding tests will be skipped
>>> + * if we fail to allocate (huge) pages.
>>> + */
>>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>>> + IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
>>> + has_transparent_hugepage()) {
>>> + page = alloc_pages(GFP_KERNEL | __GFP_NOWARN,
>>> + HPAGE_PUD_SHIFT - PAGE_SHIFT);
>>
>> Please drop __GFP_NOWARN and instead use something like alloc_contig_pages()
>> when required allocation order exceed (MAX_ORDER - 1). Else the test might
>> not be able to execute on platform configurations, where PUD THP is enabled.
>>
>
> Yes, It's correct that alloc_contig_pages() should be used here, depending
> on CONFIG_CONTIG_ALLOC. Otherwise, alloc_pages(...__GFP_NOWARN...) is still
> used as we're doing. This snippet will be changed like below in v4:
First 'order > (MAX_ORDER - 1)' needs to be established before calling into
alloc_contig_pages() without __GFP_NOWARN and set a new flag indicating that
there is contig page allocated. But if 'order <= (MAX_ORDER - 1)', then call
alloc_pages(..) without __GFP_NOWARN. There is no need to add __GFP_NOWARN
in any case. In case CONFIG_CONTIG_ALLOC is not available, directly return a
NULL as that would have been the case with alloc_pages(...__GFP_NOWARN...) as
well.
Symbol alloc_contig_pages() is not available outside CONFIG_CONTIG_ALLOC. So
IS_ENABLED() construct will not work, unless there is an empty stub added in
the header. Otherwise #ifdef CONFIG_CONTIG_ALLOC needs to be used instead.
Regardless please do test this on a x86 platform with PUD based THP in order
to make sure every thing works as expected.
>
> /*
> * Allocate (huge) pages because some of the tests need to access
> * the data in the pages. The corresponding tests will be skipped
> * if we fail to allocate (huge) pages.
> */
> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
> IS_ENABLED(CONFIG_CONTIG_ALLOC)) &&
> has_transparent_hugepage()) {
> page = alloc_contig_pages((1 << (HPAGE_PUD_SHIFT - PAGE_SHIFT)),
> GFP_KERNEL | __GFP_NOWARN,
> first_online_node, NULL);
> if (page) {
> args->is_contiguous_pud_page = true;
> args->pud_pfn = page_to_pfn(page);
> args->pmd_pfn = args->pud_pfn;
> args->pte_pfn = args->pud_pfn;
> return 0;
> }
> }
>
> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
> has_transparent_hugepage()) {
> page = alloc_pages(GFP_KERNEL | __GFP_NOWARN,
> HPAGE_PUD_SHIFT - PAGE_SHIFT);
> if (page) {
> args->is_contiguous_pud_page = false;
> args->pud_pfn = page_to_pfn(page);
> args->pmd_pfn = args->pud_pfn;
> args->pte_pfn = args->pud_pfn;
> return 0;
> }
> }
>
> [... The logic to allocate PMD huge page or page is kept as of being]
IIRC it is also not guaranteed that PMD_SHIFT <= (MAX_ORDER - 1). Hence
this same scheme should be followed for PMD level allocation as well.
> [... The code to release the PUD huge page needs changes based on @args->is_contiguous_pud_page]
Right, a flag would be needed to call the appropriate free function.
