linux-kernel - Re: [PATCH v5 00/13] KVM/X86: Introduce a new guest mapping interface

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Date:   Wed, 23 Jan 2019 13:16:39 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com
Subject: Re: [PATCH v5 00/13] KVM/X86: Introduce a new guest mapping interface

On Wed, Jan 09, 2019 at 10:42:00AM +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. Patch 2 is additionally fixing an
> incorrect page release and marking the page as dirty (i.e. as a side-effect of
> using the helper function to write).
> 
> 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.

Where could one find this patchset?

Also is there an simple test-case (or a writeup) you have for testing
this code? Specifically I am thinking about the use-case of "memory
without the 'struct page'"

And thank you for posting this patchset. It was a pleasure reviewing the
code!