linux-kernel - Re: [PATCH 2/2] kvm: Use huge pages for DAX-backed files

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Date:   Wed, 14 Nov 2018 04:09:47 -0500 (EST)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     Barret Rhoden <brho@...gle.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, yu c zhang <yu.c.zhang@...el.com>,
        yi z zhang <yi.z.zhang@...el.com>
Subject: Re: [PATCH 2/2] kvm: Use huge pages for DAX-backed files


> > As this patch is dependent on PageReserved patch(which is in progress),
> > just
> > wondering if we are able to test the code path for hugepage with DAX.
> 
> For testing, I used the following patch.  It's not 100%, since it
> intercepts at kvm_is_reserved_pfn(), and not PageReserved() directly.
> The only difference is with kvm_set_pfn_dirty() I think.
> 

Yes, this should be ok.

Thanks,
Pankaj 

> I also have a nasty module that would dump the EPT's and the host page
> table's mappings so I could confirm that the huge pages are being mapped
> correctly.
> 
> -----------------------
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2679e476b6c3..1b394a0752a0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -148,6 +148,10 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct
> kvm *kvm,
>  
>  bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>  {
> +	// XXX hack
> +	if (is_zone_device_page(pfn_to_page(pfn)))
> +		return false;
> +
>  	if (pfn_valid(pfn))
>  		return PageReserved(pfn_to_page(pfn));
>  
> -----------------------
> 
> Thanks,
> 
> Barret
> 
>