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From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
To:     "ira.weiny@intel.com" <ira.weiny@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Sterba <dsterba@suse.cz>
CC:     "hch@infradead.org" <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        "clm@fb.com" <clm@fb.com>,
        "josef@toxicpanda.com" <josef@toxicpanda.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH V2 4/8] mm/highmem: Add VM_BUG_ON() to mem*_page() calls
Thread-Topic: [PATCH V2 4/8] mm/highmem: Add VM_BUG_ON() to mem*_page() calls
Thread-Index: AQHW/3WAW9SwnELN/EW61EsEJOsRXA==
Date:   Wed, 10 Feb 2021 06:57:30 +0000
Message-ID: <BYAPR04MB4965E51F07F1AB084BC1FA84868D9@BYAPR04MB4965.namprd04.prod.outlook.com>
References: <20210210062221.3023586-1-ira.weiny@intel.com>
 <20210210062221.3023586-5-ira.weiny@intel.com>
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On 2/9/21 22:25, ira.weiny@intel.com wrote:=0A=
> From: Ira Weiny <ira.weiny@intel.com>=0A=
>=0A=
> Add VM_BUG_ON bounds checks to ensure the newly lifted and created page=
=0A=
> memory operations do not result in corrupted data in neighbor pages and=
=0A=
> to make them consistent with zero_user().[1][2]=0A=
>=0A=
I did not understand this, in my tree :-=0A=
=0A=
zero_user()=0A=
 -> zero_user_segments()=0A=
=0A=
which uses BUG_ON(), the commit log says add VM_BUG_ON(), isn't that=0A=
inconsistent withwhat is there in zero_user_segments() which uses BUG_ON() =
?=0A=
=0A=
Also, this patch uses BUG_ON() which doesn't match the commit log that says=
=0A=
ADD VM_BUG_ON(),=0A=
=0A=
Did I interpret the commit log wrong ?=0A=
=0A=
[1]=0A=
 void zero_user_segments(struct page *page, unsigned start1, unsigned end1,=
=0A=
365                 unsigned start2, unsigned end2)=0A=
366 {=0A=
367         unsigned int=0A=
i;                                                                         =
  =0A=
=0A=
368=0A=
369         BUG_ON(end1 > page_size(page) || end2 > page_size(page));=0A=
370=0A=
371         for (i =3D 0; i < compound_nr(page); i++) {=0A=
372                 void *kaddr =3D NULL;=0A=
373 =0A=
374                 if (start1 < PAGE_SIZE || start2 < PAGE_SIZE)=0A=
375                         kaddr =3D kmap_atomic(page + i);=0A=
376=0A=
377                 if (start1 >=3D PAGE_SIZE) {=0A=
378                         start1 -=3D PAGE_SIZE;=0A=
379                         end1 -=3D PAGE_SIZE;=0A=
380                 } else {=0A=
381                         unsigned this_end =3D min_t(unsigned, end1,=0A=
PAGE_SIZE);=0A=
382        =0A=
383                         if (end1 > start1)=0A=
384                                 memset(kaddr + start1, 0, this_end -=0A=
start1);=0A=
385                         end1 -=3D this_end;=0A=
386                         start1 =3D 0;=0A=
387                 }=0A=
388=0A=
389                 if (start2 >=3D PAGE_SIZE) {=0A=
390                         start2 -=3D PAGE_SIZE;=0A=
391                         end2 -=3D PAGE_SIZE;=0A=
392                 } else {=0A=
393                         unsigned this_end =3D min_t(unsigned, end2,=0A=
PAGE_SIZE);=0A=
394 =0A=
395                         if (end2 > start2)=0A=
396                                 memset(kaddr + start2, 0, this_end -=0A=
start2);=0A=
397                         end2 -=3D this_end;=0A=
398                         start2 =3D 0;=0A=
399                 }=0A=
400        =0A=
401                 if (kaddr) {=0A=
402                         kunmap_atomic(kaddr);=0A=
403                         flush_dcache_page(page + i);=0A=
404                 }=0A=
405        =0A=
406                 if (!end1 && !end2)=0A=
407                         break;=0A=
408         }=0A=
409        =0A=
410         BUG_ON((start1 | start2 | end1 | end2) !=3D 0);=0A=
411 }=0A=
412 EXPORT_SYMBOL(zero_user_segments);=0A=
=0A=
=0A=
=0A=