linux-kernel - Re: [PATCH RFC 0/3] Fix KVM misinterpreting Reserved page as an MMIO page

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Message-ID: <20181204065914.GB73736@tiger-server>
Date:   Tue, 4 Dec 2018 14:59:15 +0800
From:   Yi Zhang <yi.z.zhang@...ux.intel.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     dan.j.williams@...el.com, pbonzini@...hat.com, brho@...gle.com,
        kvm@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dave.jiang@...el.com, yu.c.zhang@...el.com, pagupta@...hat.com,
        david@...hat.com, jack@...e.cz, hch@....de, rkrcmar@...hat.com,
        jglisse@...hat.com
Subject: Re: [PATCH RFC 0/3] Fix KVM misinterpreting Reserved page as an MMIO
 page

On 2018-12-03 at 11:25:20 -0800, Alexander Duyck wrote:
> I have loosely based this patch series off of the following patch series
> from Zhang Yi:
> https://lore.kernel.org/lkml/cover.1536342881.git.yi.z.zhang@linux.intel.com
> 
> The original set had attempted to address the fact that DAX pages were
> treated like MMIO pages which had resulted in reduced performance. It
> attempted to address this by ignoring the PageReserved flag if the page
> was either a DEV_DAX or FS_DAX page.
> 
> I am proposing this as an alternative to that set. The main reason for this
> is because I believe there are a few issues that were overlooked with that
> original set. Specifically KVM seems to have two different uses for the
> PageReserved flag. One being whether or not we can pin the memory, the other
> being if we should be marking the pages as dirty or accessed. I believe
> only the pinning really applies so I have split the uses of
> kvm_is_reserved_pfn and updated the function uses to determine support for
> page pinning to include a check of the pgmap to see if it supports pinning.
kvm is not the only one users of the dax page.

A similar user of PageReserved to look at is:
 drivers/vfio/vfio_iommu_type1.c:is_invalid_reserved_pfn(
vfio is also want to know the page is capable for pinning.

I throught that you have removed the reserved flag on the dax page

in https://patchwork.kernel.org/patch/10707267/

is something I missing here?

> 
> ---
> 
> Alexander Duyck (3):
>       kvm: Split use cases for kvm_is_reserved_pfn to kvm_is_refcounted_pfn
>       mm: Add support for exposing if dev_pagemap supports refcount pinning
>       kvm: Add additional check to determine if a page is refcounted
> 
> 
>  arch/x86/kvm/mmu.c        |    6 +++---
>  drivers/nvdimm/pfn_devs.c |    2 ++
>  include/linux/kvm_host.h  |    2 +-
>  include/linux/memremap.h  |    5 ++++-
>  include/linux/mm.h        |   11 +++++++++++
>  virt/kvm/kvm_main.c       |   34 +++++++++++++++++++++++++---------
>  6 files changed, 46 insertions(+), 14 deletions(-)
> 
> --