linux-kernel - Re: [PATCH V4 4/4] kvm: add a check if pfn is from NVDIMM pmem.

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Date:   Wed, 29 Aug 2018 06:15:48 -0400 (EDT)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     Zhang Yi <yi.z.zhang@...ux.intel.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>,
        dave jiang <dave.jiang@...el.com>,
        yu c zhang <yu.c.zhang@...el.com>, david@...hat.com,
        jack@...e.cz, hch@....de, linux-mm@...ck.org, rkrcmar@...hat.com,
        jglisse@...hat.com, yi z zhang <yi.z.zhang@...el.com>
Subject: Re: [PATCH V4 4/4] kvm: add a check if pfn is from NVDIMM pmem.


> 
> 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 identify 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.
> 
> 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;
>  }

Acked-by: Pankaj Gupta <pagupta@...hat.com>

> --
> 2.7.4
> 
>