linux-kernel - Re: [RFC 03/12] KVM/VMX: Use the new host mapping API for virtual_apic

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Message-ID: <CALMp9eQPLwT5Fd2J_uKpW0OymbL6RQ1bSbsU=xXwbfP=sBFs9g@mail.gmail.com>
Date:   Fri, 9 Feb 2018 14:55:47 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     KarimAllah Ahmed <karahmed@...zon.com>
Cc:     KarimAllah Ahmed <karahmed@...zon.de>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RFC 03/12] KVM/VMX: Use the new host mapping API for virtual_apic_page

On Fri, Feb 9, 2018 at 4:15 AM, KarimAllah Ahmed <karahmed@...zon.com> wrote:

> Can you elaborate a bit? I do not really understand what is the concern.

I can't find the posting that gave me this impression. The only thing
I can find is the following in Documentation/vm/highmem.txt:

 (*) kmap().  This permits a short duration mapping of a single page.  It needs
     global synchronization, but is amortized somewhat.  It is also prone to
     deadlocks when using in a nested fashion, and so it is not recommended for
     new code.

What constitutes a "short duration," and does this new usage qualify?