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Subject: Re: [PATCH] vmap(): don't allow invalid pages
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Ding Tianhong <dingtianhong@huawei.com>,
        Alexey Klimov <aklimov@redhat.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Uladzislau Rezki <urezki@gmail.com>
References: <20220118235244.540103-1-yury.norov@gmail.com>
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From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <5b62ed03-8da8-a94d-cc48-a8cac1eae1c9@arm.com>
Date:   Thu, 20 Jan 2022 09:07:11 +0530
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On 1/19/22 10:52 PM, Yury Norov wrote:
>> Why should not this just scan over the entire user provided struct page
>> array and make sure that all pages there in are valid via above method,
>> but in vmap() itself before calling vmap_pages_range(). Because seems
>> like a single invalid page detected in vmap_pages_pte_range() will
>> anyways abort the entire vmap(). This will also enable us to drop the
>> existing NULL check above.
>
> I can do this, but why is it any better than the current approach?

Because it will just return on the first instance where the valid page
check fails, saving us some CPU cycles and an incomplete mapping ?