KVM: kvm_clear_guest_page(): fix empty_zero_page usage

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=8a3caa6d74597c2a083f7c87f866891a0b12540b
Commit:     8a3caa6d74597c2a083f7c87f866891a0b12540b
Parent:     521ee0cfb876dd31ce4e0878e1163fe0817a7acc
Author:     Heiko Carstens <heiko.carstens at de.ibm.com>
AuthorDate: Mon Nov 18 10:35:55 2013 +0100
Committer:  Gleb Natapov <gleb at redhat.com>
CommitDate: Thu Nov 21 11:19:32 2013 +0200

    KVM: kvm_clear_guest_page(): fix empty_zero_page usage
    
    Using the address of 'empty_zero_page' as source address in order to
    clear a page is wrong. On some architectures empty_zero_page is only the
    pointer to the struct page of the empty_zero_page.  Therefore the clear
    page operation would copy the contents of a couple of struct pages instead
    of clearing a page.  For kvm only arm/arm64 are affected by this bug.
    
    To fix this use the ZERO_PAGE macro instead which will return the struct
    page address of the empty_zero_page on all architectures.
    
    Signed-off-by: Heiko Carstens <heiko.carstens at de.ibm.com>
    Signed-off-by: Gleb Natapov <gleb at redhat.com>
---
 virt/kvm/kvm_main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 662f34c..a0aa84b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1615,8 +1615,9 @@ EXPORT_SYMBOL_GPL(kvm_read_guest_cached);
 
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
 {
-	return kvm_write_guest_page(kvm, gfn, (const void *) empty_zero_page,
-				    offset, len);
+	const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
+
+	return kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest_page);