linux-kernel - Re: [PATCH 3/3] kvm: add a function to check if page is from NVDIMM pmem.

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Date:   Mon, 9 Jul 2018 14:36:27 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Zhang,Yi" <yi.z.zhang@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.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, linux-mm@...ck.org, rkrcmar@...hat.com,
        yi.z.zhang@...el.com
Subject: Re: [PATCH 3/3] kvm: add a function to check if page is from NVDIMM
 pmem.

On Thu 05-07-18 21:19:30, Zhang,Yi wrote:
> 
> 
> On 2018年07月04日 23:25, Paolo Bonzini wrote:
> > On 04/07/2018 17:30, 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.
> >>
> >> Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> >> Signed-off-by: Zhang Yu <yu.c.zhang@...ux.intel.com>
> >> ---
> >>  virt/kvm/kvm_main.c | 17 +++++++++++++++--
> >>  1 file changed, 15 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >> index afb2e6e..1365d18 100644
> >> --- a/virt/kvm/kvm_main.c
> >> +++ b/virt/kvm/kvm_main.c
> >> @@ -140,10 +140,23 @@ __weak void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> >>  {
> >>  }
> >>  
> >> +static bool kvm_is_nd_pfn(kvm_pfn_t pfn)
> >> +{
> >> +	struct page *page = pfn_to_page(pfn);
> >> +
> >> +	return is_zone_device_page(page) &&
> >> +		((page->pgmap->type == MEMORY_DEVICE_FS_DAX) ||
> >> +		 (page->pgmap->type == MEMORY_DEVICE_DEV_DAX));
> >> +}
> > If the mm people agree, I'd prefer something that takes a struct page *
> > and is exported by include/linux/mm.h.  Then KVM can just do something like
> >
> > 	struct page *page;
> > 	if (!pfn_valid(pfn))
> > 		return true;
> >
> > 	page = pfn_to_page(pfn);
> > 	return PageReserved(page) && !is_dax_page(page);
> >
> > Thanks,
> >
> > Paolo
> Yeah, that could be much better. Thanks for your comments Paolo.
> 
> Hi Kara, Do u have Any opinions/ideas to add such definition in mm?

What Paolo suggests sounds good to me.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR