kvm: Introduce kvm_write_guest_offset_cached()

It allows us to update some status or field of a structure partially.

We can also save a kvm_read_guest_cached() call if we just update one
fild of the struct regardless of its current value.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: benh@kernel.crashing.org
Cc: boqun.feng@gmail.com
Cc: borntraeger@de.ibm.com
Cc: bsingharora@gmail.com
Cc: dave@stgolabs.net
Cc: jgross@suse.com
Cc: kernellwp@gmail.com
Cc: konrad.wilk@oracle.com
Cc: linuxppc-dev@lists.ozlabs.org
Cc: mpe@ellerman.id.au
Cc: paulmck@linux.vnet.ibm.com
Cc: paulus@samba.org
Cc: rkrcmar@redhat.com
Cc: virtualization@lists.linux-foundation.org
Cc: will.deacon@arm.com
Cc: xen-devel-request@lists.xenproject.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1478077718-37424-8-git-send-email-xinhui.pan@linux.vnet.ibm.com
[ Typo fixes. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 01c0b9cc3915cf7b74054516e16fc43fe9fbcafb..6f0023797b3316e2a0b5a94c845fd43718deed97 100644 (file)
--- 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 5c360347a1e9fc2091f5abf0bbb6a3432e13add9..2f38ce55016fae318134a05286ba3f0654644558 100644 (file)
--- 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,