linux-kernel - Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check

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Message-ID: <CA+CK2bA7Xz0Zg5phsQi3mhnp+_PHLAAGRLgFTQNw1FjBHaXsHA@mail.gmail.com>
Date:   Mon, 15 Feb 2021 14:30:14 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Tyler Hicks <tyhicks@...ux.microsoft.com>,
        James Morris <jmorris@...ei.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Mike Rapoport <rppt@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map
 boundaries during hotplug check

> Can't we simply use signed arithmetic here? This expression works fine
> if the quantities are all interpreted as s64 instead of u64

I was thinking about that, but I do not like the idea of using sign
arithmetics for physical addresses. Also, I am worried that someone in
the future will unknowingly change it to unsigns or to phys_addr_t. It
is safer to have start explicitly set to 0 in case of wrap.