linux-kernel - [PATCH V2 4/4] kvm: add a check if pfn is from NVDIMM pmem.

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Message-Id: <a698775099ea814c60672172030f79f0d6098b27.1531241281.git.yi.z.zhang@linux.intel.com>
Date:   Wed, 11 Jul 2018 01:04:08 +0800
From:   Zhang Yi <yi.z.zhang@...ux.intel.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, pbonzini@...hat.com,
        dan.j.williams@...el.com, jack@...e.cz, hch@....de,
        yu.c.zhang@...el.com
Cc:     linux-mm@...ck.org, rkrcmar@...hat.com, yi.z.zhang@...el.com,
        Zhang Yi <yi.z.zhang@...ux.intel.com>
Subject: [PATCH V2 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 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>
---
 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 afb2e6e..77e6ba8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -142,8 +142,12 @@ __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