linux-kernel - Re: [PATCH v4 00/14] KVM/X86: Introduce a new guest mapping interface

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Message-ID: <20181206160156.GB25299@char.us.oracle.com>
Date:   Thu, 6 Dec 2018 11:01:56 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     rkrcmar@...hat.com, pbonzini@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        jmattson@...gle.com
Subject: Re: [PATCH v4 00/14] KVM/X86: Introduce a new guest mapping interface

On Mon, Dec 03, 2018 at 10:30:53AM +0100, KarimAllah Ahmed wrote:
> Guest memory can either be directly managed by the kernel (i.e. have a "struct
> page") or they can simply live outside kernel control (i.e. do not have a
> "struct page"). KVM mostly support these two modes, except in a few places
> where the code seems to assume that guest memory must have a "struct page".
> 
> This patchset introduces a new mapping interface to map guest memory into host
> kernel memory which also supports PFN-based memory (i.e. memory without 'struct
> page'). It also converts all offending code to this interface or simply
> read/write directly from guest memory.
> 
> As far as I can see all offending code is now fixed except the APIC-access page
> which I will handle in a seperate series along with dropping
> kvm_vcpu_gfn_to_page and kvm_vcpu_gpa_to_page from the internal KVM API.
> 
> The current implementation of the new API uses memremap to map memory that does
> not have a "struct page". This proves to be very slow for high frequency
> mappings. Since this does not affect the normal use-case where a "struct page"
> is available, the performance of this API will be handled by a seperate patch
> series.

How (if any) does it affect performance?

Thanks!