[Xen-devel] [PATCH v6 07/11] KVM: Introduce kvm_write_guest_offset_cached

[Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxx>
---
 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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