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Date:   Fri, 28 Oct 2016 04:11:23 -0400
From:   Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, xen-devel-request@...ts.xenproject.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org, x86@...nel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        mingo@...hat.com, peterz@...radead.org, paulmck@...ux.vnet.ibm.com,
        will.deacon@....com, kernellwp@...il.com, jgross@...e.com,
        pbonzini@...hat.com, bsingharora@...il.com, boqun.feng@...il.com,
        borntraeger@...ibm.com, rkrcmar@...hat.com,
        David.Laight@...LAB.COM, Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Subject: [PATCH v6 07/11] KVM: Introduce kvm_write_guest_offset_cached

It allows us to update some status or field of one struct partially.

We can also save one kvm_read_guest_cached if we just update one filed
of the struct regardless of its current value.

Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 20 ++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 01c0b9c..6f00237 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -645,6 +645,8 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
 		    unsigned long len);
 int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 			   void *data, unsigned long len);
+int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+			   void *data, int offset, unsigned long len);
 int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 			      gpa_t gpa, unsigned long len);
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2907b7b..95308ee 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1972,30 +1972,38 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 }
 EXPORT_SYMBOL_GPL(kvm_gfn_to_hva_cache_init);
 
-int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
-			   void *data, unsigned long len)
+int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+			   void *data, int offset, unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	int r;
+	gpa_t gpa = ghc->gpa + offset;
 
-	BUG_ON(len > ghc->len);
+	BUG_ON(len + offset > ghc->len);
 
 	if (slots->generation != ghc->generation)
 		kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa, ghc->len);
 
 	if (unlikely(!ghc->memslot))
-		return kvm_write_guest(kvm, ghc->gpa, data, len);
+		return kvm_write_guest(kvm, gpa, data, len);
 
 	if (kvm_is_error_hva(ghc->hva))
 		return -EFAULT;
 
-	r = __copy_to_user((void __user *)ghc->hva, data, len);
+	r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
 	if (r)
 		return -EFAULT;
-	mark_page_dirty_in_slot(ghc->memslot, ghc->gpa >> PAGE_SHIFT);
+	mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(kvm_write_guest_offset_cached);
+
+int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+			   void *data, unsigned long len)
+{
+	return kvm_write_guest_offset_cached(kvm, ghc, data, 0, len);
+}
 EXPORT_SYMBOL_GPL(kvm_write_guest_cached);
 
 int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
-- 
2.4.11

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