On 29.09.2009, at 15:25, Avi Kivity wrote:
On 09/29/2009 11:17 AM, Alexander Graf wrote:
On 29.09.2009, at 11:14, Avi Kivity wrote:
On 09/29/2009 10:18 AM, Alexander Graf wrote:
With big endian userspace, we can't quite figure out if a pointer
is 32 bit (shifted>> 32) or 64 bit when we read a 64 bit pointer.
This is what happens with dirty logging. To get the pointer
interpreted
correctly, I just make it bounce twice, but admittedly that is not
ideal.
I'm open for suggestions here.
How about adding a new union member to struct kvm_dirty_log:
__u64 dirty_bitmap_virt;
And modifying userspace to write to that one?
Yes - old userspace will still build and work (we don't remove the
old field) on little endian or BE32, new userspace will work on all
flavours. We need new userspace anyway to take advantage of dirty
logging.
How about this one? (broken whitespace!)
From c3864a2c5e1fccff7839e47f12c09d9739ca441e Mon Sep 17 00:00:00 2001
From: Alexander Graf <agraf@xxxxxxx>
Date: Thu, 23 Jul 2009 21:05:57 +0200
Subject: [PATCH] Enable 32bit dirty log pointers on 64bit host
With big endian userspace, passing a pointer from 32-bit userspace to
64-bit kernel space breaks.
This is what happens with dirty logging. To get the pointer interpreted
correctly, we can just check the guest's 32bit flag and treat the
pointer
as 32 bits then.
Signed-off-by: Alexander Graf <agraf@xxxxxxx>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e27b7a9..00f2c59 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -703,6 +703,7 @@ int kvm_get_dirty_log(struct kvm *kvm,
int r, i;
int n;
unsigned long any = 0;
+ void *target_bm;
r = -EINVAL;
if (log->slot >= KVM_MEMORY_SLOTS)
@@ -718,8 +719,15 @@ int kvm_get_dirty_log(struct kvm *kvm,
for (i = 0; !any && i < n/sizeof(long); ++i)
any = memslot->dirty_bitmap[i];
+#if defined(__BIG_ENDIAN) && defined(CONFIG_64BIT)
+ /* Need to convert user pointers */
+ if (test_thread_flag(TIF_32BIT))
+ target_bm = (void*)((u64)log->dirty_bitmap >> 32);
+ else
+#endif
+ target_bm = log->dirty_bitmap;
r = -EFAULT;
- if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
+ if (copy_to_user(target_bm, memslot->dirty_bitmap, n))
goto out;
if (any)
--
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