linux-kernel - Re: [PATCH V2 0/4] Fix kvm misconceives NVDIMM pages as reserved mmio

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Date:   Fri, 20 Jul 2018 10:32:19 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Zhang,Yi" <yi.z.zhang@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        dan.j.williams@...el.com, jack@...e.cz, hch@....de,
        yu.c.zhang@...el.com, dave.jiang@...el.com
Cc:     linux-mm@...ck.org, rkrcmar@...hat.com, yi.z.zhang@...el.com
Subject: Re: [PATCH V2 0/4] Fix kvm misconceives NVDIMM pages as reserved mmio

On 20/07/2018 16:11, Zhang,Yi wrote:
> Added Jiang,Dave,
> 
> Ping for further review, comments.

I need an Acked-by from the MM people to merge this.  Jan, Dan?

Paolo

> 
> Thanks All
> 
> Regards
> Yi.
> 
> 
> On 2018年07月11日 01:01, Zhang Yi wrote:
>> For device specific memory space, when we move these area of pfn to
>> memory zone, we will set the page reserved flag at that time, some of
>> these reserved for device mmio, and some of these are not, such as
>> NVDIMM pmem.
>>
>> Now, we map these dev_dax or fs_dax pages to kvm for DIMM/NVDIMM
>> backend, since these pages are reserved. the check of
>> kvm_is_reserved_pfn() misconceives those pages as MMIO. Therefor, we
>> introduce 2 page map types, MEMORY_DEVICE_FS_DAX/MEMORY_DEVICE_DEV_DAX,
>> to indentify these pages are from NVDIMM pmem. and let kvm treat these
>> as normal pages.
>>
>> Without this patch, Many operations will be missed due to this
>> mistreatment to pmem pages. For example, a page may not have chance to
>> be unpinned for KVM guest(in kvm_release_pfn_clean); not able to be
>> marked as dirty/accessed(in kvm_set_pfn_dirty/accessed) etc.
>>
>> V1:
>> https://lkml.org/lkml/2018/7/4/91
>>
>> V2:
>> *Add documentation for MEMORY_DEVICE_DEV_DAX memory type in comment block
>> *Add is_dax_page() in mm.h to differentiate the pages is from DAX device.
>> *Remove the function kvm_is_nd_pfn().
>>
>> Zhang Yi (4):
>>   kvm: remove redundant reserved page check
>>   mm: introduce memory type MEMORY_DEVICE_DEV_DAX
>>   mm: add a function to differentiate the pages is from DAX device
>>     memory
>>   kvm: add a check if pfn is from NVDIMM pmem.
>>
>>  drivers/dax/pmem.c       |  1 +
>>  include/linux/memremap.h |  9 +++++++++
>>  include/linux/mm.h       | 12 ++++++++++++
>>  virt/kvm/kvm_main.c      | 16 ++++++++--------
>>  4 files changed, 30 insertions(+), 8 deletions(-)
>>
> 
>