(2010/04/12 2:21), Avi Kivity wrote:
On 04/09/2010 12:38 PM, Takuya Yoshikawa wrote:
By this patch, bitmap allocation is replaced with do_mmap() and
bitmap manipulation is replaced with *_user() functions.
Note that this does not change the APIs between kernel and user space.
To get more advantage from this hack, we need to add a new interface
for triggering the bitmap swith and getting the bitmap addresses: the
addresses is in user space and we can export them to qemu.
I would like to merge the new API together with the patchset, since
without it, the improvement is insufficient.
OK, it would be only a simple API functions.
TODO:
1. We want to use copy_in_user() for 32bit case too.
Definitely. Why doesn't it work now?
Sadly we don't have that for 32bit. We have to implement by ourselves.
I tested two temporary implementations for 32bit:
1. This version using copy_from_user() and copy_to_user() with
not nice vmalloc().
2. Loop with __get_user() and __put_user().
The result was 1 is much faster than 2.
Note that this is only for the compatibility issue: in the future,
we hope, qemu will not need to use this ioctl.
2. We have to implement test_bit_user() to avoid extra set_bit.
This was important in the days of shadow paging. I'm not so sure about
it with nested paging, since we'll typically only fault a page once per
iteration. Since we're very likely to actually write these days, the
extra access is wasteful.
Nice news for me! So all we need to ask x86(asm-generic) people to merge are:
set bit user and copy_in_user 32bit version.
+int kvm_arch_create_dirty_bitmap(struct kvm_memory_slot *memslot)
+{
+ unsigned long user_addr1;
+ unsigned long user_addr2;
+ int dirty_bytes = kvm_dirty_bitmap_bytes(memslot);
+
+ down_write(¤t->mm->mmap_sem);
+ user_addr1 = do_mmap(NULL, 0, dirty_bytes,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, 0);
+ if (IS_ERR((void *)user_addr1)) {
+ up_write(¤t->mm->mmap_sem);
+ return PTR_ERR((void *)user_addr1);
+ }
+ user_addr2 = do_mmap(NULL, 0, dirty_bytes,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, 0);
+ if (IS_ERR((void *)user_addr2)) {
+ do_munmap(current->mm, user_addr1, dirty_bytes);
+ up_write(¤t->mm->mmap_sem);
+ return PTR_ERR((void *)user_addr2);
+ }
+ up_write(¤t->mm->mmap_sem);
I think a single do_mmap() call for both bitmaps is simpler in terms of
error handling.
OK, I'll fix in the next version.
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