From: Dan Williams <dan.j.williams@intel.com>
To: Zhang Yi <yi.z.zhang@linux.intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>,
"KVM list" <kvm@vger.kernel.org>,
"Zhang, Yu C" <yu.c.zhang@intel.com>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
"Jan Kara" <jack@suse.cz>, "David Hildenbrand" <david@redhat.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Linux MM" <linux-mm@kvack.org>,
rkrcmar@redhat.com, "Paolo Bonzini" <pbonzini@redhat.com>,
"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH V5 4/4] kvm: add a check if pfn is from NVDIMM pmem.
Date: Tue, 18 Sep 2018 19:53:32 -0700 [thread overview]
Message-ID: <CAPcyv4ifg2BZMTNfu6mg0xxtPWs3BVgkfEj51v1CQ6jp2S70fw@mail.gmail.com> (raw)
In-Reply-To: <4e8c2e0facd46cfaf4ab79e19c9115958ab6f218.1536342881.git.yi.z.zhang@linux.intel.com>
On Fri, Sep 7, 2018 at 2:25 AM Zhang Yi <yi.z.zhang@linux.intel.com> 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 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@linux.intel.com>
> Acked-by: Pankaj Gupta <pagupta@redhat.com>
> ---
> virt/kvm/kvm_main.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index c44c406..9c49634 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -147,8 +147,20 @@ __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);
> +
> + /*
> + * For device specific memory space, there is a case
> + * which we need pass MEMORY_DEVICE_FS[DEV]_DAX pages
> + * to kvm, these pages marked reserved flag as it is a
> + * zone device memory, we need to identify these pages
> + * and let kvm treat these as normal pages
> + */
> + return PageReserved(page) && !is_dax_page(page);
Should we consider just not setting PageReserved for
devm_memremap_pages()? Perhaps kvm is not be the only component making
these assumptions about this flag?
Why is MEMORY_DEVICE_PUBLIC memory specifically excluded?
This has less to do with "dax" pages and more to do with
devm_memremap_pages() established ranges. P2PDMA is another producer
of these pages. If either MEMORY_DEVICE_PUBLIC or P2PDMA pages can be
used in these kvm paths then I think this points to consider clearing
the Reserved flag.
That said I haven't audited all the locations that test PageReserved().
Sorry for not responding sooner I was on extended leave.
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next prev parent reply other threads:[~2018-09-19 2:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 18:03 [PATCH V5 0/4] Fix kvm misconceives NVDIMM pages as reserved mmio Zhang Yi
2018-09-07 17:04 ` Ahmed S. Darwish
2018-09-18 14:31 ` Yi Zhang
2018-09-07 18:03 ` [PATCH V5 1/4] kvm: remove redundant reserved page check Zhang Yi
2018-09-07 18:03 ` [PATCH V5 2/4] mm: introduce memory type MEMORY_DEVICE_DEV_DAX Zhang Yi
2018-09-07 18:03 ` [PATCH V5 3/4] mm: add a function to differentiate the pages is from DAX device memory Zhang Yi
2018-09-07 18:04 ` [PATCH V5 4/4] kvm: add a check if pfn is from NVDIMM pmem Zhang Yi
2018-09-19 2:53 ` Dan Williams [this message]
2018-09-19 7:20 ` David Hildenbrand
2018-09-20 22:49 ` Yi Zhang
2018-09-20 21:19 ` Dan Williams
2018-09-21 22:47 ` Yi Zhang
2018-09-21 14:23 ` David Hildenbrand
2018-09-21 18:17 ` Dan Williams
2018-09-21 19:29 ` David Hildenbrand
2018-10-19 16:33 ` Barret Rhoden
2018-10-22 8:47 ` Yi Zhang
2018-09-19 10:55 ` [PATCH V5 0/4] Fix kvm misconceives NVDIMM pages as reserved mmio Yi Zhang
2018-09-19 2:43 ` Pankaj Gupta
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