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SubjectRe: [PATCH V2 4/8] mm/highmem: Add VM_BUG_ON() to mem*_page() calls
Date
On 2/9/21 22:25, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Add VM_BUG_ON bounds checks to ensure the newly lifted and created page
> memory operations do not result in corrupted data in neighbor pages and
> to make them consistent with zero_user().[1][2]
>
I did not understand this, in my tree :-

zero_user()
-> zero_user_segments()

which uses BUG_ON(), the commit log says add VM_BUG_ON(), isn't that
inconsistent withwhat is there in zero_user_segments() which uses BUG_ON() ?

Also, this patch uses BUG_ON() which doesn't match the commit log that says
ADD VM_BUG_ON(),

Did I interpret the commit log wrong ?

[1]
void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
365 unsigned start2, unsigned end2)
366 {
367 unsigned int
i;

368
369 BUG_ON(end1 > page_size(page) || end2 > page_size(page));
370
371 for (i = 0; i < compound_nr(page); i++) {
372 void *kaddr = NULL;
373
374 if (start1 < PAGE_SIZE || start2 < PAGE_SIZE)
375 kaddr = kmap_atomic(page + i);
376
377 if (start1 >= PAGE_SIZE) {
378 start1 -= PAGE_SIZE;
379 end1 -= PAGE_SIZE;
380 } else {
381 unsigned this_end = min_t(unsigned, end1,
PAGE_SIZE);
382
383 if (end1 > start1)
384 memset(kaddr + start1, 0, this_end -
start1);
385 end1 -= this_end;
386 start1 = 0;
387 }
388
389 if (start2 >= PAGE_SIZE) {
390 start2 -= PAGE_SIZE;
391 end2 -= PAGE_SIZE;
392 } else {
393 unsigned this_end = min_t(unsigned, end2,
PAGE_SIZE);
394
395 if (end2 > start2)
396 memset(kaddr + start2, 0, this_end -
start2);
397 end2 -= this_end;
398 start2 = 0;
399 }
400
401 if (kaddr) {
402 kunmap_atomic(kaddr);
403 flush_dcache_page(page + i);
404 }
405
406 if (!end1 && !end2)
407 break;
408 }
409
410 BUG_ON((start1 | start2 | end1 | end2) != 0);
411 }
412 EXPORT_SYMBOL(zero_user_segments);




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