linux-kernel - Re: [PATCH V3 4/4] kvm: add a check if pfn is from NVDIMM pmem.

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Date:   Tue, 14 Aug 2018 01:32:05 +0800
From:   "Zhang,Yi" <yi.z.zhang@...ux.intel.com>
To:     Pankaj Gupta <pagupta@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, pbonzini@...hat.com,
        dan j williams <dan.j.williams@...el.com>, jack@...e.cz,
        hch@....de, yu c zhang <yu.c.zhang@...el.com>, linux-mm@...ck.org,
        rkrcmar@...hat.com, yi z zhang <yi.z.zhang@...el.com>
Subject: Re: [PATCH V3 4/4] kvm: add a check if pfn is from NVDIMM pmem.



On 2018年08月09日 16:32, Pankaj Gupta 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
> s/indentify/identify & remove '.'
Thanks Pankaj, :-)
>
>> 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
>>
>> Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
>> ---
>>  virt/kvm/kvm_main.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index c44c406..969b6ca 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -147,8 +147,12 @@ __weak void
>> kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
>>  
>>  bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>>  {
>> -        if (pfn_valid(pfn))
>> -                return PageReserved(pfn_to_page(pfn));
>> +        struct page *page;
>> +
>> +        if (pfn_valid(pfn)) {
>> +                page = pfn_to_page(pfn);
>> +                return PageReserved(page) && !is_dax_page(page);
>> +        }
>>  
>>          return true;
>>  }
>> --
>> 2.7.4
>>
>>